Apparatus for manufacturing bonded substrate

ABSTRACT

The present invention provides an apparatus for manufacturing a bonded substrate that suppresses a defect in the bonded substrate. When the pressure in a vacuum chamber is at the atmospheric level, upper and lower chuck units respectively attract substrates through vacuum. When the vacuum chamber is depressurized, each chuck unit electrostatically attracts the associated substrate. During the depressurization of the vacuum chamber, the pressure for attracting each substrate to the associated chuck unit is controlled to be equal to the pressure in the vacuum chamber. This prevents each substrate from falling from or moving relative to the associated chuck unit. The first and second substrates are thus bonded together and accurately aligned.

This is a Continuation of patent application Ser. No. 11/248,741, filedOct. 12, 2005 now U.S. Pat. No. 7,300,532, which is a Divisional ofpatent application Ser. No. 09/998,054, filed Nov. 30, 2001 now U.S.Pat. No. 7,096,911.

BACKGROUND OF THE INVENTION

The present invention relates to apparatuses for manufacturing bondedsubstrates, and, more particularly, to apparatuses for manufacturingpanel displays that have a predetermined gap between a pair ofsubstrates, for example, liquid crystal displays (LCDs).

Panel displays such as LCDs with larger display areas are now beingdeveloped. Further, to improve the resolution, an increased pixel countper unit area is demanded in the panel displays. Accordingly, anapparatus for manufacturing panel displays with bonded substrates mustbe capable of accurately aligning the substrates even if each substrateis relatively large.

FIG. 1 is a plan view showing a portion of a prior art, active-matrixtype liquid crystal panel display 10, as viewed from a color filtersubstrate.

The liquid crystal panel display 10 includes an array substrate 11 and acolor filter (CF) substrate 16. The array substrate 11 has a pluralityof pixel areas 12 that are formed in a matrix-like manner. Each pixelarea 12 includes a switch element, or a thin film transistor (TFT) 13.The pixel areas 12 form a display area 14. A gate electrode of each TFT13 is connected to a gate line (not shown). A drain electrode of eachTFT 13 is connected to a data line (not shown). A source electrode ofeach TFT 13 is connected to a pixel electrode (not shown) formed in eachpixel area 12. A plurality of data lines and gate lines are located atthe periphery of the array substrate 11 and are connected to a terminalportion 15. The terminal portion 15 is connected to an external drivesource (not shown).

The CF substrate 16 is smaller than the array substrate 11 by an areathat substantially corresponds to the area of the terminal portion 15.The CF substrate 16 is spaced from the array substrate 11 at apredetermined interval. A cell gap is formed between the CF substrate 16and the array substrate 11 and is filled with liquid crystal. Thedimension of the cell gap (the cell thickness) is thus substantiallyequal to the interval between the CF substrate 16 and the arraysubstrate 11. The CF substrate 16 includes a common electrode (notshown) and a black matrix (BM) 17, or a shielding film such as a colorfilter (red (R), green (G), or blue (B)) and a chrome film. The BM 17 islocated at a position corresponding to certain pixel areas 12 in thedisplay area 14 to form a contrast and shields each TFT 13, thussuppressing a light leak current. A BM periphery 18 shields the displayarea 14 from unnecessary light from the exterior. The array substrate 11is bonded with the CF substrate 16 through a seal 19 that containsthermosetting resin.

A procedure for manufacturing a liquid crystal display mainly includesan array step, a cell step, and a module step. The array step includesformation of a wiring pattern and the switch elements (TFTs) 13 (in thecase of an active-matrix type display) on each glass substrate 11, 16.The cell step includes alignment of liquid crystal, installation ofspacers, and filling of liquid crystal in the cell gap between thesubstrates 11, 16. The module step includes installation of a driver ICand a backlight.

Conventionally, liquid crystal is filed in the cell gap in accordancewith a vacuum method. In the method, the array substrate 11, which hasthe TFTs 13, is bonded with an opposed substrate, or the CF substrate16, through the seal 19 located between the substrates 11, 16. After theseal 19 is hardened, the liquid crystal and the substrates 11, 16 aresupplied to a depressurized treatment chamber. An inlet is formed in theseal 19, and the substrates 11, 16 are placed in the treatment chamberto immerse the inlet in the liquid crystal. The pressure in thetreatment chamber is then increased to the atmospheric level. Thisintroduces the liquid crystal into the gap between the substrates 11,16. Subsequently, the inlet is sealed.

The liquid crystal may be filled in the cell gap in accordance with adrip method. In that method, the seal 19 is placed around the arraysubstrate 11 in a frame-like shape. A predetermined amount of liquidcrystal is then dripped on the array substrate 11. Subsequently, thearray substrate 11 is bonded with the CF substrate 16 underdepressurization. In this state, liquid crystal develops in the cell gapto fill the gap. As compared to the vacuum method, the drip methodrequires less liquid crystal and shortens the time consumed for theoperation. This lowers the cost for manufacturing the panel display andimproves mass-productivity.

However, an apparatus for manufacturing a panel display in accordancewith the drip method has the following problems.

[1: Deformed Substrates, Display Defects, and Insufficient SubstrateAttraction]

A conventional apparatus for manufacturing a bonded substrate holds eachsubstrate 11, 16 with a vacuum chuck, an electrostatic chuck, or amechanical chuck.

More specifically, when the vacuum chuck is used, each substrate 11, 16is placed on an attraction side of a parallel surface plate. The vacuumchuck attracts a corresponding side of each substrate 11, 16 throughvacuum, thus holding the substrate 11, 16. In this state, an appropriateamount of liquid crystal is dripped on the array substrate 11 with adispenser. Subsequently, the CF substrate 16 is aligned with the arraysubstrate 11, and the substrates 11, 16 are bonded together in adepressurized treatment chamber.

However, if the treatment chamber is depressurized sufficiently, theholding performance of the vacuum chuck is lowered and the vacuum chuckcannot hold each substrate 11, 16 in a stable manner. To avoid this, thetreatment chamber cannot be depressurized optimally. Accordingly,sufficient pressure for bonding the substrates 11, 16 together does notact on each substrate 11, 16. As a result, the substrates 11, 16 arebonded together non-uniformly, thus causing a display defect in aresulting product.

The mechanical chuck holds the array substrate 11 and the CF substrate16 with an engagement piece, such as a holder and a ring. In this case,the reactive force to the holding force of the mechanical chuck actsonly in a limited part of each substrate 11, 16. This deforms thesubstrates 11, 16. Thus, the substrates 11, 16 are not located parallelwith each other when bonding the substrates 11, 16 together. If thesubstrates 11, 16 are bonded in this state, the substrates 11, 16 aremisaligned. This reduces the aperture ratio of each pixel (TFT) 13 orcauses a problem such as a light leakage from a shielded portion.

In the case of the electrostatic chuck, voltage is supplied between anelectrode formed on a parallel surface plate and a conductive filmformed on each glass substrate 11, 16. This generates a Coulomb forcebetween each glass substrate 11, 16 and the associated electrode toattract the glass substrate 11, 16 to the associated electrostaticchuck. The glass substrates 11, 16 are then placed in the treatmentchamber as opposed to each other. The treatment chamber is thendepressurized to bond the substrates 11, 16 together. However, in thiscase, glow discharge occurs between the opposed substrates 11, 16 duringthe depressurization of the treatment chamber. This damages a circuit orTFTs formed on each substrate 11, 16, thus causing a defective product.Further, if air is trapped between each substrate 11, 16 and theassociated electrostatic chuck, the substrate 11, 16 may separate fromthe chuck during the depressurization of the treatment chamber.

[2: Damaged Liquid Crystal and Misaligned Substrates]

Conventionally, the seal 19 is formed of photoresist material thathardens in a relatively short time or thermosetting photoresist materialthat hardens when exposed to light and heat. However, when irradiatingUV light to the seal 19 for hardening the seal 19, the liquid crystal inthe vicinity of the seal 19 is also exposed to the light. This causesdisplay non-uniformness near the boundary between the seal 19 and theliquid crystal.

Further, when the seal 19 is exposed to the liquid crystal before beinghardened completely, a component of the seal 19 may elute into theliquid crystal, thus contaminating the same. To avoid this, an intenseUV light may be used to irradiate to the seal 19 to rapidly harden theseal 19. However, in this case, the UV light is diffused by thesubstrates 11, 16, thus exposing the liquid crystal to the light.

Generally, exposure of liquid crystal to the UV light changes propertiesof the liquid crystal. Particularly, the substance's specific resistanceis reduced. The liquid crystal thus cannot meet a requirement that anLCD with TFTs should have a relatively high voltage maintaining rate.That is, a liquid crystal cell's drive voltage in the exposed displayportion is varied with respect to that in the non-exposed displayportion, for example, the middle of the panel display. This causesdisplay non-uniformness, particularly in half tone.

FIG. 2 shows a prior art panel display 10. The panel display 10 has aspacer frame 20 located along the periphery of each substrate 11, 16.The spacer frame 20 prevents the seal 19 in a non-hardened state frombeing exposed to liquid crystal 21. However, if an excessive amount ofliquid crystal is filled in the gap between the substrates 11, 16, theliquid crystal flows from the gap through the spacer frame 20 (see FIG.3). In this case, the seal 19, which is not yet hardened, is exposed tothe liquid crystal, for example, at positions 22. Each dot in FIG. 3corresponds to a position at which the liquid crystal 21 is dripped.

The substrates 11, 16 are bonded together under depressurization. Thus,if the substrates 11, 16 are exposed to the atmospheric pressure, themiddle of each substrate 11, 16 is deformed, thus forming a spacebetween the spacer frame 20 and the substrates 11, 16. In this case, theseal 19 is exposed to the liquid crystal 21, which is wet.

Further, even after the substrates 11, 16 are thermally hardened, areactive force due to original waviness and warp of each substrate 11,16 remains acting on the substrate 11, 16. Thus, if the seal 19 isformed of photoresist thermosetting material, the reactive force may bereleased when heating the substrates 11, 16 that are hardened. Thismisaligns the substrates 11, 16.

Also, there may be a change in the environment or condition of eachsubstrate 11, 16 after the bonded substrates 11, 16 are exposed to theatmospheric pressure for hardening the seal 19. Further, when formingthe cell gap, the substrates 11, 16 may be held in an unstable manner ormay be distorted. In these cases, the opposed substrates 11, 16 arebonded together as misaligned, thus leading to a defect in the cell gap.Accordingly, it is complicated to manufacture the panel display 10 in astable manner.

[3: Non-Uniform Cell Thickness and its Effects on Substrates]

To distribute liquid crystal uniformly between the substrates 11, 16,the substance must be dripped at a plurality of positions of thesubstrate 11. However, since the amount of liquid crystal supplied tothe substrate 11 is relatively small as a whole, the drip amount foreach drip position must be adjusted accurately. Further, if there is anenvironmental change, for example, a temperature variation, theviscosity or volume of liquid crystal is altered. Also, drip performancemay be varied among dispensers (drip devices). These factors vary thedrip amount for each drip position, and the resulting cell thicknessbecomes non-uniform.

FIGS. 4A, 4B, 4C are cross-sectional views for illustrating uniform ornon-uniform cell thickness of a liquid crystal panel display. In theliquid crystal panel display of FIG. 4A, an optimal amount of liquidcrystal is supplied between the substrates 11, 16. The panel displaythus has a desired cell thickness. More specifically, the arraysubstrate 11 is optimally bonded with the CF substrate 16 through theseal 19. A plurality of spacer beads 23 ensures a predetermined cellthickness.

As shown in FIG. 4B, if an excessive amount of liquid crystal issupplied between the substrates 11, 16, the seal 19 is not pressed to atarget dimension. This causes display non-uniformness near the peripheryof the panel display.

If a further excessive amount of liquid crystal is supplied between thesubstrates 11, 16, not only the seal 19 is insufficiently pressed, butalso the middle of the panel display is expanded, as shown in FIG. 4C.In this state, display non-uniformness is caused in the entire paneldisplay.

[4: Undesired Exposure of Substrates to Liquid Crystal]

Each substrate 11, 16 includes an alignment mark of several micrometers.As described, the substrates 11, 16 are bonded together underdepressurization after liquid crystal is dripped on the substrate 11.During the bonding, the substrates 11, 16 are aligned based on a cameraimage of the alignment marks such that the substrate 16 is not exposedto the liquid crystal on the substrate 11. If the exposure occurs, theliquid crystal adheres to the substrate 16, thus causing a non-uniformcell gap in the resulting panel display or exposure of the seal 19 tothe liquid crystal.

Generally, the substrates 11, 16 must be bonded together with theaccuracy of an order of several micrometers. Thus, a lens with arelatively long focus distance is needed to view the alignment marks ofboth substrates 11, 16 at the same time, if the substrates 11, 16 arespaced from each other. However, this lens has a complicated structureand is sometimes unavailable. This makes the bonding proceduredifficult, and a defect may be caused in the bonded substrates 11, 16.

[5: Non-Uniform Pressing of Substrates]

When bonding the substrates 11, 16 together, the opposed substrates 11,16 are pressed to each other to obtain a predetermined cell thickness.Thus, each substrate 11, 16 must be maintained parallel with each other,and an equal pressure must be applied to the substrates 11, 16. Morespecifically, after dripping liquid crystal on the substrate 11, thesubstrates 11, 16 are pressed to each other in a vacuum treatmentchamber. However, a pressing device, such as a hydraulic cylinder, islocated outside the treatment chamber and is exposed to the atmosphericair. Thus, the atmospheric pressure corresponding to the introductioncross-sectional area of the pressing device acts on the pressed surfaceof each substrate 11, 16. Generally, the relationship between theoperational amount of the pressing device and the pressure of thepressing device applied to each substrate 11, 16 is predeterminedthrough an experiment. The pressure of the pressing device is controlledin accordance with this relationship. However, for example, aging of thepressing device may alter the pressure applied to the substrates 11, 16.This hampers reproducibility of the bonding. Further, the substrates 11,16 may not be sufficiently pressed to each other.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide anapparatus for manufacturing a bonded substrate that suppresses a defectin a resulting product.

To achieve the foregoing and other objectives and in accordance with thepurpose of the present invention, the invention provides an apparatusfor manufacturing a bonded substrate. The apparatus includes a treatmentchamber and first and second holding units, which oppose each other inthe treatment chamber. The first and second holding units respectivelyhold first and second substrates. At least one holding unit generatespressure to attract the associated substrate through vacuum. Theapparatus further includes a vacuum pump, which depressurizes thetreatment chamber, and a control device, which controls the treatmentchamber, the first and second holding units, and the vacuum pump. Thecontrol device instructs each holding unit to attract the associatedsubstrate through vacuum, depressurizes the treatment chamber, andsubstantially equalizes the pressure applied by at least one holdingunit with the pressure in the treatment chamber.

A further perspective of the present invention is a method for bonding afirst substrate with a second substrate in a treatment chamber, whichaccommodates a first holding unit that attracts the first substrate anda second holding unit that attracts the second substrate. The methodincludes the steps of transporting the first and second substrates as apair to the treatment chamber, attracting each substrate to theassociated holding unit through vacuum by applying pressure to thesubstrate, depressurizing the treatment chamber, and substantiallyequalizing the pressure applied to each substrate with the pressure inthe treatment chamber.

Other aspects and advantages of the invention will become apparent fromthe following description, taken in conjunction with the accompanyingdrawings, illustrating by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

FIG. 1 is a partial view showing a prior art liquid crystal paneldisplay;

FIG. 2 is a cross-sectional view showing another prior art liquidcrystal panel display;

FIG. 3 is a view schematically showing a liquid crystal panel displayfabricated in accordance with a prior art process;

FIGS. 4A, 4B, and 4C are cross-sectional views each showing a liquidcrystal panel display fabricated in accordance with a prior art process;

FIG. 5 is a block diagram schematically showing an embodiment of abonding apparatus according to the present invention;

FIG. 6 is a view schematically showing a transport device of FIG. 5;

FIG. 7 is a view schematically showing a liquid crystal drip device ofFIG. 5;

FIGS. 8A, 8B, 8C, 8D are views each schematically showing a dispenser ofFIG. 7;

FIG. 9 is a diagram schematically showing dripping of liquid crystal;

FIG. 10 is a view schematically showing a transport device thattransports a substrate to a vacuum chamber;

FIG. 11 is a view schematically showing the vacuum chamber and anelectrostatic chuck;

FIGS. 12A and 12B are views schematically showing an attraction side ofthe electrostatic chuck, and FIGS. 12C and 12D are views schematicallyshowing a flat plate of FIG. 21;

FIGS. 13A and 13B are cross-sectional views schematically showing theelectrostatic chuck;

FIGS. 14A and 14B are block diagrams showing an equivalent circuit ofthe electrostatic chuck;

FIG. 15 is a timing chart showing variation in waveforms of voltageapplied to the electrostatic chuck;

FIGS. 16A, 16B, and 16C are views schematically showing a process forseparating substrates;

FIG. 17 is a view schematically showing an alignment device;

FIG. 18 is a view explaining an alignment control procedure;

FIG. 19 is a view schematically showing a pressing device;

FIG. 20 is a perspective view showing a chuck unit;

FIG. 21 is a view schematically showing a transport device thattransports a substrate to a seal hardening device;

FIG. 22 is a view schematically showing a seal hardening device;

FIGS. 23A and 23B are views schematically showing a bending correctionmechanism;

FIGS. 24A and 24B are views explaining bending of a substrate;

FIGS. 25A, 25B, 25C, 25D, and 25E are views explaining a method forcorrecting the bending of the substrate;

FIG. 26 is a view schematically showing a modification of the transportdevice of FIG. 10;

FIG. 27 is a view schematically showing a modification of the alignmentdevice of FIG. 17;

FIGS. 28A, 28B, and 28C are views each showing a modification of theattraction side of FIG. 12A;

FIG. 29 is a view explaining correction of the alignment device;

FIG. 30 is a view schematically showing a bonded substrate manufacturingapparatus of another embodiment according to the present invention;

FIGS. 31A, 31B, and 31C are views explaining alignment marks;

FIG. 32 is a view explaining another alignment control procedure;

FIGS. 33A, 33B, 33C, 33D and 33E are views explaining another alignmentcontrol procedure;

FIG. 34 is a view showing another corrective transport operation;

FIG. 35 is a view schematically showing another chamber;

FIG. 36 is a view schematically showing a prior art in correspondencewith FIG. 35;

FIG. 37 is a view schematically showing a prior art in correspondencewith FIG. 35; and

FIG. 38 is a view schematically showing another seal hardening device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A bonded substrate manufacturing apparatus 30 of an embodiment accordingto the present invention will now be described with reference to FIGS. 5to 22.

FIG. 5 is a view schematically showing the apparatus 30 that is used ina cell step of a process for fabricating a liquid crystal panel display.In the cell step, liquid crystal is dripped on a substrate, and thesubstrate is bonded with an opposed substrate.

In the liquid crystal panel display fabricated with the bonded substratemanufacturing apparatus 30, liquid crystal is filled in the gap betweena first substrate W1 and a second substrate W2. If the panel display isan active matrix type, the first substrate W1 is a glass array substratethat includes switch elements such as TFTs, and the second substrate W2is a color filter (CF) substrate that includes a color filter or ashielding film. The first substrate W1 and the second substrate W2 arefabricated in separate steps and are supplied to the apparatus 30. Aseal is applied on a side of the first or second substrate W1, W2 (inthis embodiment, the first substrate W1) along its periphery in aframe-like shape.

The apparatus 30 includes a main controller 31, a seal applying device32, a liquid crystal drip device 33, a bonding device 34, an inspectiondevice 35, and a plurality of transport devices 38 a, 38 b, 38 c, 38 d.The transport devices 38 a-38 d transport the first and secondsubstrates W1, W2. The main controller 31 controls the devices 32-38.The bonding device 34 includes a pressing device 36 and a hardeningdevice 37 that are controlled by the main controller 31. The maincontroller 31 controls the transport devices 38 a-38 d and transportrobots to transport the first and second substrates W1, W2.

More specifically, the seal applying device 32 first receives the firstand second substrates W1, W2. The seal applying device 32 then appliesseal material on the upper side of the first or second substrate W1, W2(for example, the glass substrate W1) along its circumference. Anadhesive including a photo-curing adhesive is used as the seal material.

Subsequently, the transport device 38 a receives the first substrate W1and the corresponding second substrate W2 from the seal applying device32 and transports the substrates W1, W2 to the drip device 33 as a pair.

The drip device 33 receives the first and second substrates W1, W2 anddrips liquid crystal at a plurality of positions on a side of the firstsubstrate W1 on which a seal is applied. Afterward, the transport device38 b transports the first and second substrates W1, W2 to the pressingdevice 36.

As shown in FIG. 11, the pressing device 36 has a vacuum chamber 71. Thevacuum chamber 71 includes a first or lower chuck unit 72 b and a secondor upper chuck unit 72 a. When the lower and upper chuck units 72 b, 72a attract the first substrate W1 and the second substrate W2,respectively, the vacuum chamber 71 is depressurized.

Subsequently, a prescribed gas is supplied to the vacuum chamber 71 forpretreatment. The gas includes exciting gas (reaction gas) for excitingplasma panel displays and replacement gas, such as nitrogen gas(inactive gas). In the pretreatment, impurities adhered on thesubstrates W1, W2 or a display element are exposed to the reaction gasand the replacement gas for a predetermined time.

The pretreatment stabilizes the quality of the bonding surfaces of thesubstrates W1, W2, which cannot be separated once the substrates W1, W2are bonded together. More specifically, an oxide film formed on eachsubstrate W1, W2 or a foreign object adhered to the substrate W1, W2alters the surface state of the substrate W1, W2. The alteration isnon-uniform among the substrates W1, W2, thus hampering stablefabrication of panel displays. However, the pretreatment suppressesformation of the oxide film and adhesion of the foreign object andremoves impurities from the substrates W1, W2. This maintains thesurface of each substrate W1, W2 in a predetermined state and stabilizesthe quality of a product.

Each substrate W1, W2 includes an alignment mark. The pressing device 36optically detects the alignment marks and aligns the first and secondsubstrates W1, W2 without contacting the substrates W1, W2, such that anopposed side of the second substrate W2 is not exposed to the seal andliquid crystal applied on the first substrate W1. The pressing device 36then applies a predetermined pressure to the first and second substratesW1, W2 in the vacuum chamber 71, thus pressing the substrates W1, W2 toeach other to obtain a predetermined cell thickness. Afterward, thepressing device 36 increases the pressure in the vacuum chamber 71 tothe atmospheric level and then opens the vacuum chamber 71.

The main controller 31 measures the time that elapses after the vacuumchamber 71 receives the first and second substrates W1, W2, thuscontrolling the time for which the substrates W1, W2 are exposed to thegases in the vacuum chamber 71 (the time from when the vacuum chamber 71receives the substrates W1, W2 to when the substrates W1, W2 are bondedtogether). In this manner, the quality of the bonding surface of eachsubstrate W1, W2 is maintained in a stable state after the substratesW1, W2 are bonded together.

Subsequently, the transport device 38 c transports the pressedsubstrates W1, W2 from the pressing device 36 to the hardening device37. More specifically, the main controller 31 starts to measure the timewhen the pressing of the first and second substrates W1, W2 iscompleted. After a predetermined time, the main controller 31 activatesthe transport device 38 c to transport the first and second substratesW1, W2 from the pressing device 36 to the hardening device 37. Thehardening device 37 receives the first and second substrates W1, W2 andirradiates light of a predetermined wavelength to the substrates W1, W2,thus hardening the seal. A liquid crystal panel display is thusfabricated.

As described, when the predetermined time elapses after the first andsecond substrates W1, W2 are pressed together, the light for hardeningthe seal is irradiated to the first and second substrates W1, W2. Thetime is varied in relation to diffusion speed of liquid crystal and thetime needed for completely releasing reactive force generated againstthe pressing of the substrates W1, W2. The time is determined through anexperiment.

The liquid crystal filled in the gap between the first and secondsubstrates W1, W2 diffuses or develops when the substrates W1, W2 arepressed together and then are exposed to the atmospheric air. Thus, itis preferred that the aforementioned time is shorter than the timeneeded for the liquid crystal to completely diffuse and reach the seal.In this case, the seal is completely hardened by the time the seal isexposed to the liquid crystal.

The first and second substrates W1, W2 are deformed due to reactiveforce when pressure is applied to each substrate W1, W2 to press thesubstrates W1, W2 together. Since the seal is still being hardened whenthe transport device 38 c is transporting the substrates W1, W2 to thehardening device 37, the reactive force is released from the first andsecond substrates W1, W2 during this period. Accordingly, it ispreferred that the aforementioned time is longer than the time requiredfor completely releasing the reactive force. In this case, by the timethe seal reaches the hardening device 37, the reactive force has beenreduced. This prevents the first and second substrates W1, W2 from beingmisaligned.

After the seal hardens, the transport device 38 d transports the liquidcrystal panel display to the inspection device 35. The inspection device35 inspects the liquid crystal panel display for misalignment betweenthe first and second substrates W1, W2. That is, the inspection device35 detects a misalignment direction and a misalignment amount of eachsubstrate W1, W2. The inspection device 35 informs the main controller31 of the result.

In accordance with the result, the main controller 31 corrects thealignment of the pressing device 36. In other words, before pressing thefirst and second substrates W1, W2 together, the substrates W1, W2 arelocated offset from each other in accordance with the detectedmisalignment amount in an opposite direction to the detectedmisalignment direction. This cancels the misalignment between the firstand second substrates W1, W2. In this manner, a panel display with thealigned substrates W1, W2 is obtained in a subsequent operation cycle.

The main controller 31 includes a transport controller 48 and a robotcontroller 49 of FIG. 6, a drip controller 53 of FIG. 7, a temperaturecontroller 60 of FIG. 8A, an attraction controller 84 of FIG. 11, analignment controller 114 of FIG. 17 or 27, a load controller 137 of FIG.19, and an irradiation controller 150 of FIG. 22.

The drip device 33, the bonding device 34, the inspection device 35, thepressing device 36, the hardening device 37, and the transport devices38 a-38 d will now be described in detail.

First, the transport device 38 a, 38 b will be described with referenceto FIG. 6. The transport device 38 a includes a slider 41 that moves atray 42 in a transport direction. The tray 42 receives the firstsubstrate W1 and the second substrate W2 that includes electrodes andTFTs or a color filter. More specifically, each substrate W1, W2 isplaced on the tray 42 such that the side that includes the electrodesfaces upward. The first and second substrates W1, W2 each has anidentification code (for example, a bar code) I1, I2, respectively, fordistinguishing the substrates W1, W2 from each other.

As described, the first and second substrates W1, W2 are fabricated inseparate steps before being supplied to the transport device 38 a. Thetransport device 38 a transports one first substrate W1 and acorresponding second substrate W2 as a pair to the drip device 33. Thefirst and second substrates W1, W2 thus reach the bonding device 34.This prevents the bonding device 34 from receiving only one substrate W1or W2 and suspending its operation, thus improving efficiency formanufacturing liquid crystal panel displays.

The transport device 38 b includes a slider 43 and a pair of transportrobots 44, 45. The slider 43 moves the tray 42 in a predetermineddirection. The transport robots 44, 45 receive the first and secondsubstrates W1, W2, respectively. One transport robot (44 or 45) reversesthe associated substrate (W1 or W2) such that the electrode side of thefirst substrate W1 opposes the electrode side of the second substrateW2. In this embodiment, the transport robot 45 reverses the secondsubstrate W2, which does not include the seal. The transport robots 44,45 then transport the first and second substrates W1, W2 to the pressingdevice 36 as opposed to each other.

More specifically, the main controller 31 includes a pair of ID codereaders 46, 47, the transport controller 48, and the robot controller49. The ID code readers 46, 47 read out the ID codes I1, I2 of the firstand second substrates W1, W2, respectively, and inform the transportcontroller 48 of the result. In accordance with the result, thetransport controller 48 selects the substrate to be reversed (in thisembodiment, the second substrate W2) and informs the robot controller 49of the selection.

As described, the transport robots 44, 45 receive the first and secondsubstrates W1, W2, respectively. Thus, in accordance with the selectionof the transport controller 48, the robot controller 49 controls thetransport robot 45 to reverse the substrate W2. Accordingly, theelectrode side of the first substrate W1 opposes the electrode side ofthe second substrate W2. The robot controller 49 then controls thetransport robots 44, 45 to transport the first and second substrates W1,W2 to the pressing device 36.

The liquid crystal drip device 33 will be described with reference toFIGS. 7, 8, and 9.

As shown in FIG. 7, the drip device 33 includes a dispenser 51, amovement mechanism 52, the drip controller 53, and a measurement device54. The dispenser 51 includes liquid crystal. The movement mechanism 52supports the dispenser 51 and moves the dispenser 51 horizontally.

The drip controller 53 controls the dispenser 51 in accordance with asignal from the main controller 31, thus accurately dripping liquidcrystal on the first substrate W1. In other words, the drip controller53 maintains the temperature of liquid crystal in the dispenser 51 at aconstant level. The drip controller 53 controls the movement mechanism52 to move the dispenser 51 to a plurality of positions on the firstsubstrate W1. At each position, the dispenser 51 drips a predeterminedamount of liquid crystal. The drip controller 53 then moves thedispenser 51 to a position corresponding to the measurement device 54and drips liquid crystal through the dispenser 51. The measurementdevice 54 measures the weight of the liquid crystal dripped by thedispenser 51 and informs the drip controller 53 of the measurement. Thedrip controller 53 corrects the drip amount of the dispenser 51 inaccordance with the measurement such that the dispenser 51 drips aconstant amount of liquid crystal. This suppresses the temperaturevariation of liquid crystal in the dispenser 51. Further, when there isan environmental change, the drip amount of the dispenser 51 iscorrected to be the constant value.

As shown in FIG. 8A, the dispenser 51 includes a cylindrical syringe 55,a plunger 56, and a heater 58. Liquid crystal is received in the syringe55 and is discharged from the syringe 55 when pressed by a plunger 56.The heater 58 heats the liquid crystal LC. The drip controller 53controls the plunger 56 to apply a certain pressure to the liquidcrystal LC. A predetermined amount of liquid crystal LC is thus drippedfrom a nozzle 57 at the distal end of the syringe 55.

The heater 58 has a substantially annular shape and is located aroundthe outer side of the syringe 55. A thermocouple 59 is located near thedistal end of the syringe 55 to measure the temperature of the liquidcrystal LC. The heater 58 and the thermocouple 59 are connected to thetemperature controller 60 located in the drip controller 53. Thetemperature controller 60 determines the temperature of the liquidcrystal LC in accordance with a signal from the thermocouple 59 andcontrols the heater 58 to maintain the temperature of the liquid crystalLC at a constant level.

The syringe 55 includes a rotary valve 61 that has a cylindrical rotarybody 61 a. The rotary body 61 a extends through the syringe 55 in adirection perpendicular to the axis of the syringe 55. The rotary body61 a rotates around the axis of the syringe 55. As shown in FIG. 8B, avalve hole 61 b is formed in the rotary body 61 a. The diameter of thevalve hole 61 b is substantially equal to the inner diameter of thesyringe 55. The drip controller 53 controls the position at which therotary valve 61 rotates.

That is, if the drip controller 53 rotates the rotary body 61 a suchthat the axis of the valve hole 61 b corresponds to the axis of thesyringe 55, an upper section of the syringe 55 is connected integrallyto a distal section of the syringe 55. This transmits the pressure ofthe plunger 56 to the distal end of the syringe 55 without causing anyloss. The pressure acts to drip the liquid crystal LC from the nozzle57.

In contrast, if the drip controller 53 rotates the rotary body 61 a suchthat the axis of the valve hole 61 b becomes substantially perpendicularto the axis of the syringe 55, the upper section of the syringe 55 isdisconnected from the distal end of the syringe 55. This reduces thepressure applied to the liquid crystal LC by the plunger 56. Further,air is prevented from entering the syringe 55 through the nozzle 57 whenthe plunger 56 is raised. Thus, the liquid crystal LC is dripped fromthe nozzle 57 without forming bubbles.

Further, the rotary valve 61 automatically supplies the liquid crystalLC to the syringe 55. For example, a liquid crystal reservoir (notshown) is connected to a section between the plunger 56 and the rotaryvalve 61 through a supply passage. When the rotary valve 61 is closedand the plunger 56 is raised, the liquid crystal LC is introduced fromthe reservoir to the syringe 55. The liquid crystal LC is thusautomatically supplied to the syringe 55 without stopping the operationof the dispenser 51. Further, in this state, the rotary valve 61 in theclosed state prevents air from entering the syringe 55 through thenozzle 57, suppressing bubble formation. The rotary valve 61 may bereplaced by a valve body that moves horizontally and has a valve holewith a diameter substantially equal to the inner diameter of the syringe55.

An air blower 62 and an air drawer 63 are located at opposite sides ofthe nozzle 57 of the syringe 55. The air blower 62 is connected to acompressor (not shown) and has a lateral elongated outlet (see FIG. 8C).The air blower 62 blows air to form an air curtain in a directionperpendicular to the drip direction of the liquid crystal LC, or theaxis of the nozzle 57. The air curtain blows away excessive liquidcrystal LC from the distal end of the nozzle 57.

The air drawer 63, or an air inlet, is connected to a vacuum pump (notshown) and includes a lateral elongated inlet (see FIG. 8D). The airdrawer 63 thus draws and collects the air and the liquid crystal LCblown by the air blower 62. The air drawer 63 also draws the liquidcrystal LC from the distal end of the nozzle 57. The air flow (the aircurtain) from the air blower 62 to the air drawer 63 efficiently blowsaway the excessive liquid crystal from the distal end of the nozzle 57and collects the same. In this manner, the nozzle 57 is constantlycleaned, thus maintaining the drip amount of the liquid crystal LC asaccurate.

The drip controller 53 actuates the air blower 62 and the air drawer 63during a waiting period of the dispenser 51 (for example, when thedispenser 51 is being moved from one drip position to another for asubsequent drip). This maintains the drip amount of the liquid crystalLC as accurate. Further, the excessive liquid crystal LC is preventedfrom accidentally dripping on the corresponding side of the firstsubstrate W1.

The dispenser 51 does not necessarily have to include the air blower 62and the air drawer 63 but may include only the air drawer 63. Thisstructure also prevents the first substrate W1 from being contaminatedby the excessive liquid crystal LC. Further, the drip amount of theliquid crystal LC is maintained as accurate.

That is, the heater 58, the rotary valve 61, the air blower 62, and theair drawer 63 that are provided in the dispenser 51 form a drip amountequalizing device.

As shown in FIG. 9, the measurement device 54 is preferably anelectronic balance. The measurement device 54 measures the weight of theliquid crystal LC dripped by the dispenser 51 and informs the dripcontroller 53 of the measurement.

The drip controller 53 includes a central processing unit (CPU) 64, apulse oscillator 65, and a motor driver 66. The CPU 64 sends a controlsignal that represents the weight of the liquid crystal LC measured bythe measurement device 54 to the pulse oscillator 65. The pulseoscillator 65 generates a pulse signal in accordance with the controlsignal and sends the pulse signal to the motor driver 66. The motordriver 66 generates a drive signal for a motor 67 in accordance with thepulse signal. It is preferred that the motor 67 is a pulse motor thatselectively raises and lowers the plunger 56, depending on the drivesignal. If the motor 67 lowers the plunger 56, the liquid crystal LC isdripped. The drip amount of the liquid crystal LC thus corresponds tothe operation amount of the plunger 56.

More specifically, the CPU 64 calculates the drip amount of the liquidcrystal LC based on the measurement of the measurement device 54. TheCPU 64 then corrects the control signal to maintain the drip amount ofthe liquid crystal LC as a constant value. The CPU 64 sends thecorrected control signal to the pulse oscillator 65. This prevents thedrip amount of the liquid crystal LC from being altered due to a changein the condition (such as the viscosity) of the liquid crystal LC or achange in the operation amount of the plunger 56 (due to, for example,friction of the plunger 56 or the condition of the motor 67). The liquidcrystal LC is thus continuously dripped automatically.

The transportation of the first and second substrates W1, W2 to thepressing device 36 will be described with reference to FIG. 10.

The vacuum chamber 71 of the pressing device 36 includes an upper lid 71a and a lower lid 71 b. A drive mechanism (not shown) movably supportsthe upper lid 71 a. When the drive mechanism lifts the upper lid 71 afrom the lower lid 71 b, the vacuum chamber 71 becomes open.

As described, in the vacuum chamber 71, the upper chuck unit 72 a andthe lower chuck unit 72 b support the second substrate W2 and the firstsubstrate W1, respectively. A first movement mechanism 112 (FIG. 17)supports the upper chuck unit 72 a and selectively lifts and lowers theupper chuck unit 72 a. A second movement mechanism 113 (FIG. 17)supports the lower chuck unit 72 b and moves the lower chuck unit 72 bhorizontally (in a direction X and a direction Y). The second movementmechanism 113 also rotates the lower chuck unit 72 b horizontally (in adirection θ).

The lower lid 71 b includes a plurality of lift pins 73 that are raisedand lowered. The transport robot 44 first places the first substrate W1on the distal ends of the lift pins 73 that are held at a raisedposition. The lift pins 73 are then lowered to place the first substrateW1 on the lower chuck unit 72 b, thus allowing the lower chuck unit 72 bto attract the first substrate W1.

The upper lid 71 a includes a pair of arms 74. The transport robot 45first passes the second substrate W2 to the arms 74. In this state, theupper chuck unit 72 a attracts the second substrate W2.

The lower side of the upper chuck unit 72 a (an upper attraction side)and the upper side of the lower chuck unit 72 b (a lower attractionside), as viewed in FIG. 10, are flattened through machining. It ispreferred that the flatness of each attraction side is 100 micrometersor smaller. The attraction sides are adjusted to be parallel with eachother when the upper and lower chuck units 72 a, 72 b oppose each other.It is preferred that a parallel level between the attraction sides is 50micrometers or smaller. The term “parallel level” is defined as adimension of a space between the upper and lower attraction sides whenthe attraction sides contact each other. If the attraction sides areentirely parallel, the attraction sides form no space when contactingeach other. In this state, the parallel level is defined as zero.However, if the attraction sides are only partially parallel, a space isformed between the attraction sides. In this case, the parallel level isdefined as greater than zero. The greater the parallel level is, thelarger the space is.

Next, the operation of the upper and lower chuck units 72 a, 72 b willbe described.

As shown in FIG. 11, the upper chuck unit 72 a includes an upper holdingplate 75 a and an upper electrostatic chuck 76 a attached to the upperholding plate 75 a. An upper attraction line 77 a is formed in the upperchuck unit 72 a for attracting the second substrate W2 through vacuum(using a difference in pressure). The upper attraction line 77 aincludes a plurality of upper attraction holes, an upper horizontalpassage, and a plurality of upper discharge passages. The upperattraction holes open at the lower side, or the attraction side, of theupper electrostatic chuck 76 a. The upper horizontal passage extendslaterally in the upper holding plate 75 a and is connected to the upperattraction holes. Each upper discharge passage extends from the upperhorizontal line in an upward direction. The upper attraction line 77 ais connected to a vacuum pump 79 a through a depressurization line 78 a.A depressurization valve 80 a is located in the depressurization line 78a and is connected to the attraction controller 84.

The depressurization line 78 a is connected to the vacuum chamber 71through a pair of pressure equilibration lines 81 a. Each pressureequilibration line 81 a includes a pressure equilibration valve 82 a. Apressure sensor 83 a is located in the depressurization line 78 a. Thepressure sensor 83 a measures the pressure in the depressurization line78 a and informs the attraction controller 84 of the measurement.

The lower chuck unit 72 b includes a lower holding plate 75 b and alower electrostatic chuck 76 b attached to the lower holding plate 75 b.A lower attraction line 77 b is formed in the lower chuck unit 72 b forattracting the first substrate W1 through vacuum. The lower attractionline 77 b includes a plurality of lower attraction holes, a lowerhorizontal passage, and a plurality of lower discharge passages. Thelower attraction holes open at the upper side, or the attraction side,of the lower electrostatic chuck 76 b. The lower horizontal passageextends laterally in the lower holding plate 75 b and is connected tothe lower attraction holes. Each lower discharge passage extends fromthe lower horizontal line in a downward direction. The lower attractionline 77 b is connected to a vacuum pump 79 b through a depressurizationline 78 b. A depressurization valve 80 b is located in thedepressurization line 78 b and is connected to the attraction controller84.

The depressurization line 78 b is connected to the vacuum chamber 71through a pair of pressure equilibration lines 81 b. Each pressureequilibration line 81 b includes a pressure equilibration valve 82 b. Apressure sensor 83 b is located in the depressurization line 78 b. Thepressure sensor 83 b measures the pressure in the depressurization line78 b and informs the attraction controller 84 of the measured value.

The vacuum chamber 71 is connected to a vacuum pump 86 through a line 85that has a valve 87. The vacuum pump 86 depressurizes the vacuum chamber71. The attraction controller 84 controls the vacuum pump 86 and thevalve 87 to adjust the pressure in the vacuum chamber 71. A pressuresensor 88 is located in the vacuum chamber 71 to measure the pressure inthe vacuum chamber 71. The pressure sensor 88 is connected to theattraction controller 84.

When the attraction controller 84 actuates the vacuum pumps 79 a, 79 bto open the depressurization valves 80 a, 80 b, each depressurizationline 78 a, 78 b and the associated attraction line 77 a, 77 b aredepressurized. This attracts each substrate W2, W1 to the associatedchuck unit 72 a, 72 b through vacuum. If the attraction controller 84applies voltage to the upper and lower electrostatic chucks 76 a, 76 b,each electrostatic chuck 76 a, 76 b generates Coulomb force. The forceacts to electrostatically attract the second and first substrates W2, W1to the associated chuck units 72 a, 72 b.

The attraction controller 84 switches between a vacuum attraction modeand an electrostatic attraction mode, depending on the pressure (thevacuum level) in the vacuum chamber 71.

In other words, the attraction controller 84 opens the vacuum chamber 71to receive the first and second substrates W1, W2, as shown in FIG. 10.The attraction controller 84 then actuates the vacuum pumps 79 a, 79 b,thus enabling each chuck unit 72 a, 72 b to attract the associatedsubstrate W2, W1. Subsequently, the attraction controller 84 closes thevacuum chamber 71 and controls the vacuum pump 86 and the valve 87 toreduce the pressure in the vacuum chamber 71. The attraction controller84 detects the pressure in the vacuum chamber 71 and the pressure ineach depressurization line 78 a, 78 b in accordance with detectionsignals from the pressure sensors 83 a, 83 b, and 88. When the pressurein the vacuum chamber 71 reaches a predetermined level, the attractioncontroller 84 applies voltage to the electrostatic chucks 76 a, 76 b togenerate Coulomb force. This electrostatically attracts each substrateW2, W1 to the associated electrostatic chuck 76 a, 76 b. Before thepressure in the vacuum chamber 71 becomes equal to or lower than thepressure in each depressurization line 78 a, 78 b, or, preferably, whenthe pressure in the vacuum chamber 71 reaches the predetermined level(and the electrostatic attraction mode is started), the attractioncontroller 84 closes the depressurization valves 80 a, 80 b and opensthe pressure equilibration valves 82 a, 82 b in the pressureequilibration lines 81 a, 81 b. This equilibrates the pressure in eachdepressurization line 78 a, 78 b and the pressure in the associatedattraction line 77 a, 77 b with the pressure in the vacuum chamber 71.

If the pressure in the vacuum chamber 71 becomes lower than the pressurein each depressurization line 77 a, 77 b when each electrostatic chuck76 a, 76 b holds the associated substrate W2, W1 through vacuum, gasflows from the depressurization lines 77 a, 77 b to the vacuum chamber71. In this case, the second substrate W2 separates from the upper chuckunit 72 a, and the first substrate W1 may possibly move relative to thelower chuck unit 72 b. These problems are avoided if the attractioncontroller 84 switches between the vacuum attraction mode and theelectrostatic attraction mode in accordance with the pressure (thevacuum level) in the vacuum chamber 71.

As shown in FIGS. 12A and 12B, a plurality of attraction grooves 89 areformed in the attraction side of the upper electrostatic chuck 76 a. Theposition of each attraction groove 89 corresponds to the secondsubstrate W2 when the upper electrostatic chuck 76 a attracts thesubstrate W2. It is preferred that the depth of each groove 89 is halfof the lateral dimension of the groove 89.

Each attraction groove 89 prevents gas from being trapped between theattraction side of the upper electrostatic chuck 76 a and the secondsubstrate W2. Thus, even if the pressure in the vacuum chamber 71 isreduced, the second substrate W2 neither separates from the upperelectrostatic chuck 72 a nor moves respective to the electrostatic chuckunit 72 a.

The attraction grooves 89 are aligned parallel with each other.Accordingly, as compared the case in which the grooves 89 are arrangedin a crossed manner, waviness in the second substrate W2 is suppressed.

The attraction grooves 89 reduce the contact area between the attractionside of the upper electrostatic chuck 76 a and the second substrate W2.That is, without the grooves 89, the upper electrostatic chuck 76 aattracts and contacts the entire corresponding side of the secondsubstrate W2. In this case, if pressure is applied to the secondsubstrate W2, the second substrate W2 shrinks, thus accumulatingreactive force in the substrate W2 with respect to the attraction forceof the upper electrostatic chuck 76 a. The reactive force is releasedwhen separating the bonded substrates W2, W1 from the upperelectrostatic chuck 76 a. This misaligns the bonded substrates W1, W2.However, the attraction grooves 89 prevent the second substrate W2 fromexpanding or shrinking when the pressure is applied to the substrate W2held by the upper electrostatic chuck 76 a. As a result, the bondedsubstrates W1, W2 are maintained as aligned.

Although not illustrated, the attraction grooves 89 are formed in theattraction side of the lower electrostatic chuck 76 b, like those of theattraction side of the upper electrostatic chuck 76 a. This structureprevents the first substrate W1 from separating from or moving relativeto the lower electrostatic chuck 76 b and being deformed.

The electrostatic attraction mode of the upper electrostatic chuck 76 awill hereafter be described.

FIG. 13A is a block diagram schematically showing the electric circuitof the upper electrostatic chuck 76 a. The upper electrostatic chuck 76a includes a plurality of dielectric layers that are applied on theupper holding plate 75 a. In this embodiment, the upper electrostaticchuck 76 a has four dielectric layers, or first, second, third, andfourth dielectric layers 91 a, 91 b, 91 c, 91 d. First, second, third,and fourth electrodes 92 a, 92 b, 92 c, 92 d are embedded in the firstto fourth dielectric layers 91 a-91 d, respectively. In each dielectriclayer 91 a-91 d, the interval between the attraction side of the upperelectrostatic chuck 76 a and the associated electrode 92 a-92 d (theelectrode embedding depth) is preferably one millimeter or more.

The first and third electrodes 92 a, 92 c are connected to a firstattraction power source 93 a, and the second and fourth electrodes 92 b,92 d are connected to a second attraction power source 93 b. In otherwords, adjacent electrodes 92 a-92 d are connected to different powersources, or the first and second attraction power sources 93 a, 93 b.

The attraction controller 84 controls the first and second attractionpower sources 93 a, 93 b. The first attraction power source 93 a appliespositive voltage to the first and third electrodes 92 a, 92 c. Thesecond attraction power source 93 b applies negative voltage to thesecond and fourth electrodes 92 b, 92 d. This causes a relatively highpotential difference between the first and second electrodes 92 a, 92 band between the third and fourth electrodes 92 c, 92 d. That is, theattraction controller 84 controls the first and second attraction powersources 93 a, 93 b to vary the attraction force of the upperelectrostatic chuck 76 a in a stepped manner. This makes it easy for theupper electrostatic chuck 76 a to selectively attract and separate thesecond substrate W2.

As viewed in FIG. 13A, first and second conductive connectors 94 a, 94 bare connected to opposite lateral sides of the upper electrostatic chuck76 a, or the left side of the first dielectric layer 91 a and the rightside of the fourth dielectric layer 91 d, respectively. The firstconductive connector 94 a is connected to a switching power source 95 a.The second conductive connector 94 b is connected to a switching powersource 95 b through a switch 96.

The switch 96 includes a common terminal, a first connecting terminal,and a second connecting terminal. The common terminal is connected tothe second conductive connector 94 b. The first connecting terminal isconnected to a frame ground FG. The second connecting terminal isconnected to the switching power source 95 b.

The attraction controller 84 supplies voltage to the switching powersources 95 a, 95 b, thus controlling the output voltage of the switchingpower sources 95 a, 95 b in a stepped manner in accordance with thevoltage supply. This activates an electric charge that is generated bythe electrostatic force of the upper electrostatic chuck 76 a. Morespecifically, when separating the second substrate W2 from the upperelectrostatic chuck 76 a, the attraction controller 84 nullifies thevoltage supply. The attraction controller 84 then controls the switch 96to connect the second conductive connector 94 b to the frame ground FGor generates an electric current that flows from the switching powersource 95 b to the switching power source 95 a through the fourth tofirst dielectric layers 91 d-91 a and the first conductive connector 94a. This cancels the electric charge accumulated in the first to fourthdielectric layers 91 a-91 d during the attraction of the upperelectrostatic chuck 76 a. Accordingly, even if the interval between thesecond substrate W2 and the attraction side of the upper electrostaticchuck 76 a is increased, separation charge (discharge) is prevented frombeing caused by a rapid increase in the voltage generated by theaccumulated electric charge (or the potential difference between thesecond substrate W2 and the upper electrostatic chuck 76 a).Accordingly, the circuit components such as the TFTs and patterns formedon the second substrate W2 (and the first substrate W1), are maintainedas undamaged, thus suppressing a defect in the bonded substrates W1, W2.

FIG. 14A is a block diagram showing the equivalent circuit formed on thefirst to fourth dielectric layers 91 a-91 d, the second substrate W2,and the contact surfaces between the dielectric layers 91 a-91 d and thesecond substrate W2. Although the equivalent circuit of FIG. 14A isconsidered as infeasible for the second substrate W2 formed of asubstantially insulating material, or glass, the applicant of thepresent invention has confirmed that the second substrate W2 actuallyforms the equivalent circuit as illustrated. That is, the secondsubstrate W2 includes resistance and capacitor components. Thus,although the second substrate W2 is formed of the insulating material,the second substrate W2 is attracted to the electrostatic chuck 76 a.

FIG. 14B is a block diagram for explaining the attraction of the upperelectrostatic chuck 76 a. In the drawing, the reference index Vindicates a voltage supply, Vg indicates a voltage that acts to attractthe second substrate W2 to the upper electrostatic chuck 76 a, Rfindicates the film resistance of each dielectric layer 91 a-91 d, Rsindicates the contact resistance between each dielectric layer 91 a-91 dand the second substrate W2, and C indicates the capacitance between thesecond substrate W2 and the attraction side of the upper electrostaticchuck 76 a. The voltage Vg is obtained by the following equation:Vg=(Rs/(Rf+Rs))×V

FIG. 13B shows a modification of the electric circuit of the upperelectrostatic chuck 76 a for suppressing the separation charge. Thedrawing corresponds to the left end portion of the upper electrostaticchuck 76 a in FIG. 13A.

As shown in FIG. 13B, a conductive body 97 is embedded in a surface(attraction side) of the dielectric layer 91 a to contact the secondsubstrate W2. More specifically, the conductive body 97 is located alonga corresponding side of the second substrate W2. In this manner, asviewed in FIG. 13B, a lateral portion of the conductive body 97corresponds to the circuit component forming area (the area in which thecircuit components and wiring are located) of the second substrate W2.The conductive body 97 is connected to a frame ground FG through aswitch 98.

To separate the second substrate W2 from the upper electrostatic chuck76 a, the attraction controller 84 controls the switch 98 to connect theconductive body 97 to the frame ground FG. Accordingly, the electriccharge accumulated in the dielectric layer 91 a and the second substrateW2 during the attraction of the upper electrostatic chuck 76 a escape tothe frame ground FG. The second substrate W2 thus easily separates fromthe upper electrostatic chuck 76 a. This prevents the separation chargefrom occurring, and the second substrate W2 is prevented from beingdamaged (neither the circuit components nor the wiring of the secondsubstrate W2 are damaged).

The switch 98 may be connected to a switching power source 99 instead ofthe frame ground FG. The attraction controller 84 generates an electriccurrent that flows from the switching power source 99 to the conductivebody 97 through the switch 98, thus canceling the electric charge in thedielectric layer 91 a and the second substrate W2. Accordingly, thesecond substrate W2 separates easily from the upper electrostatic chuck76 a, thus preventing the separation charge from occurring. As a result,also in this case, the second substrate W2 is prevented from beingdamaged.

The conductive body 97 is connected to the wiring of the secondsubstrate W2 through a switch 100 and a contact pin 100 a. When theupper electrostatic chuck 76 a electrostatically attracts the secondsubstrate W2, one side of the second substrate W2 is charged positiveand the other side of the second substrate W2 is charged negative.However, since the electric charge in the second substrate W2 arecanceled when the switch 100 is turned on, the second substrate W2easily separates from the dielectric layer 91 a. Further, the separationcharge is stopped from occurring by turning on the switch 100, thuspreventing the second substrate W2 (the circuit components and wiring ofthe second substrate W2) from being damaged.

Also, the switch 98 connects the conductive body 97 selectively to theframe ground FG or the power source 99 to prevent the separation chargefrom occurring.

FIG. 15 is a timing chart showing variation in waveforms of voltagesupplied to the upper electrostatic chuck 76 a. In the chart, the solidline represents a first voltage supplied by the first and secondattraction power sources 93 a, 93 b of FIG. 13A. The first voltage isplotted along the left vertical axis (unit: kV) of the chart, as viewedin FIG. 15. The double-dotted broken line represents the voltagesupplied by the switching power sources 95 a, 95 b. This voltage isplotted along the right axis (unit: V) of the chart.

As shown in FIG. 15, in an attraction period, the attraction controller84 controls the first and second attraction power sources 93 a, 93 b tosupply the dielectric layers 91 a-91 d with the first voltage that issufficiently large to electrostatically attract the second substrate W2.Subsequently, in a preparation period, the attraction controller 84lowers the first voltage and controls the switching power sources 95 a,95 b to supply a relatively low preparation voltage to the dielectriclayers 91 a-91 d. Finally, in a separation period, the attractioncontroller 84 reduces the first voltage to a negative value and controlsthe switching power sources 95 a, 95 b to supply a relatively highseparation voltage to the dielectric layers 91 a-91 d. The separationperiod corresponds to the time needed for activating the electric chargein the dielectric layer 91 a-91 d and the second substrate W2 and isdetermined through, for example, an experiment.

In this manner, the second substrate W2 is separated from the upperelectrostatic chuck 76 a simply in accordance with the prescribedperiods. That is, it is unnecessary to detect the electric chargeaccumulated in the dielectric layers 91 a-91 d and the second substrateW2. Further, a rapid voltage increase is suppressed, and the electriccharge is prevented from remaining in the dielectric layers 91 a-91 dand the second substrate W2. This makes it easy to separate the secondsubstrate W2 from the upper electrostatic chuck 76 a. In addition, theseparation charge is stopped from occurring, thus preventing the secondsubstrate W2 (the circuit components and wiring of the second substrateW2) from being damaged.

Although not illustrated, the lower electrostatic chuck 76 b isidentical to the upper electrostatic chuck 76 a. The attractioncontroller 84 supplies voltage to the lower electrostatic chuck 76 b tocontrol the lower electrostatic chuck 76 b.

The separation of each substrate W1, W2 from the associatedelectrostatic chuck 76 b, 76 a will hereafter be described withreference to FIGS. 16A, 16B, 16C.

As shown in FIG. 16A, to press the first and second substrates W1, W2 toeach other (during the attraction period), the attraction controller 84turns on an upper switch 101 a and a lower switch 101 b. An upperattraction power source 102 a and a lower attraction power source 102 bthus supply voltage to the upper and lower electrostatic chucks 76 a, 76b, respectively. Each attraction power source 102 a, 102 b includes thefirst and second attraction power sources 93 a, 93 b of FIG. 13A.

In the preparation period, as shown in FIG. 16B, the attractioncontroller 84 turns off the upper switch 101 a, thus nullifying thevoltage supply to the upper electrostatic chuck 76 a.

In the separation period, as shown in FIG. 16C, the attractioncontroller 84 maintains the lower switch 101 b in a turned-on state andraises the upper chuck unit 72 a. In this state, the lower power source102 b continuously supplies voltage to the lower electrostatic chuck 76b. Thus, the lower chuck unit 72 b attracts the first and secondsubstrates W1, W2, thus preventing the substrates W1, W2 from movingrelative to each other. Further, the second substrate W2 easilyseparates from the upper electrostatic chuck 76 a, and the upper chuckunit 72 a easily separates from the lower chuck unit 72 b.

After raising the upper chuck unit 72 a, the attraction controller 84opens the vacuum chamber 71 of FIG. 11, thus introducing the atmosphericair to the vacuum chamber 71. In this state, the lower chuck unit 72 bcontinuously attracts the bonded substrates W1, W2 electrostatically.This prevents each substrate W1, W2 from being deformed due to thepressure variation in the vacuum chamber 71.

Next, an alignment device 36 a of the pressing device 36 will bedescribed with reference to FIGS. 17 and 18.

As shown in FIG. 17, the alignment device 36 a includes an image pickupdevice 111, the first and second movement mechanisms 112, 113, and analignment controller 114. The image pickup device 111 has first andsecond lenses 115, 116. Each lens 115, 116 has a differentmagnification. More specifically, the magnification of the first lens115 is lower than that of the second lens 116. That is, the field ofview of the first lens 115 is broader than that of the second lens 116.Further, the depth of focus and the depth of field of the first lens 115are larger than those of the second lens 116.

The first movement mechanism 112 movably supports the upper chuck unit72 a and the image pickup device 111. The first movement mechanism 112selectively raises and lowers the upper chuck unit 72 a and the imagepickup device 111. The first movement mechanism 112 constantly holds theimage pickup device 111 at a position above the upper chuck unit 72 aand maintains the vertical interval between the upper chuck unit 72 aand each lens 115, 116 at a constant value. In other words, the positionof each lens 115, 116 relative to the upper chuck unit 72 a does notchange. The depth of field of each lens 115, 116 is selected to becapable of focusing on the second substrate W2 held by the upper chuckunit 72 a and the first substrate W1 held by the lower chuck unit 72 b.

A through hole 117 extends vertical through the upper chuck unit 72 a.The first and second lenses 115, 116 are aligned in a horizontaldirection at a predetermined interval. The first movement mechanism 112horizontally moves the image pickup device 111 such that the axis of thefirst or second lens 115, 116 corresponds to the axis of the throughhole 117. In this manner, the image pickup device 111 switches betweenthe first lens 115 and the second lens 116.

The second movement mechanism 113 supports the lower chuck unit 72 b tohorizontally move the lower chuck unit 72 b (in the direction X and thedirection Y) and rotate the same in the direction θ.

The first and second substrates W1, W2 include first and secondalignment marks M1, M2, respectively. These alignment marks M1, M2 arelocated at matching positions of the substrates W1, W2. In thisembodiment, the first alignment mark M1 is a dot, while the secondalignment mark M2 is a double circle.

When the first and second substrates W1, W2 are spaced from each other,the alignment controller 114 substantially aligns the substrates W1, W2using the first lens 115, which has a relatively large depth of focus.When the first and second substrates W1, W2 are located relatively closeto each other, the alignment controller 114 precisely aligns thesubstrates W1, W2 using the second lens 116, which has a relativelysmall depth of focus. More specifically, the alignment controller 114first controls the first movement mechanism 112 to separate the upperchuck unit 72 a from the lower chuck unit 72 b at a first interval A. Inthis state, as shown in FIG. 18, the center of the first alignment markM1 is located offset from that of the second alignment mark M2, asviewed in a view 118 a of the first lens 115. Further, in the view 118a, although the second alignment mark M2 is actually the double circle,the second alignment mark M2 appears to be a single circle due to therelatively low magnification of the first lens 115. The alignmentcontroller 114 controls the second movement mechanism 113 such that thecenter of the first alignment mark M1 corresponds to that of the secondalignment mark M2 (as viewed in a view 118 b).

The first interval A is selected such that the field of view of thefirst lens 115 reliably includes the first and second alignment marksM1, M2. The first interval A is determined through an experiment or thelike. When each chuck unit 72 a, 72 b receives the associated substrateW1, W2, the position of each substrate W1, W2 relative to the associatedchuck unit 72 a, 72 b is varied due to, for example, a dimension error.The amount of the variation is determined through an experiment or anoperation test. Further, regardless of the variation, the first intervalA and the field of view (the magnification) of the first lens 115 areselected to reliably include the first and second alignment marks M1, M2in the field of view of the first lens 115.

Subsequently, the alignment controller 114 controls the first movementmechanism 112 to lower the upper chuck unit 72 a and the image pickupdevice 111 such that the upper chuck unit 72 a is spaced from the lowerchuck unit 72 b at a second interval B. The second interval B is shorterthan the first interval A. Further, the alignment controller 114horizontally moves the image pickup device 111 such that the axis of thesecond lens 116 corresponds to the axis of the through hole 117. In thisstate, as shown in FIG. 18, the center of the first alignment mark M1 islocated offset from that of the second alignment mark M2, as viewed in aview 119 a of the second lens 116. The alignment controller 114 thuscontrols the second movement mechanism 113 such that the center of thefirst alignment mark M1 corresponds to that of the second alignment markM2 (as viewed in a view 119 b of the second lens 116).

Next, the alignment controller 114 controls the first movement mechanism112 to lower the upper chuck unit 72 a and the image pickup device 111such that the upper chuck unit 72 a is spaced from the lower chuck unit72 b at a third interval C. The third interval C is shorter than thesecond interval B. The third interval C is selected to prevent thesecond substrate W2 from being exposed to the seal and liquid crystalapplied on the first substrate W1. As shown in FIG. 18, the center ofthe first alignment mark M1 is located offset from that of the secondalignment mark M2, as viewed in a view 120 a of the second lens 116. Thealignment controller 114 thus controls the second movement mechanism 113such that the center of the first alignment mark M1 corresponds to thatof the second alignment mark M2 (as viewed in a view 120 b of the secondlens 116).

Even if the center of the first alignment mark M1 corresponds to that ofthe second alignment mark M2, as viewed in the view 120 b (when theupper chuck unit 72 a is spaced from the lower chuck unit 72 b at thethird interval C), the first and second substrates W1, W2 may beactually misaligned. The third interval C is thus selected to containthe misalignment amount in an acceptable range.

As described, the image pickup device 111 switches between the firstlens 115 and the second lens 116. Further, the interval between thefirst and second substrates W1, W2 is adjusted in accordance with thedepth of focus of each lens 115, 116. Accordingly, the image pickupdevice 111 aligns the first and second substrates W1, W2 withoutcontacting the substrates W1, W2 such that the misalignment amountbetween the substrates W1, W2 falls in the acceptable range.

A pressing mechanism 36 c of the pressing device 36 will now bedescribed with reference to FIG. 19. FIG. 19 is a side view showing thepressing mechanism 36 c. The pressing mechanism 36 c applies pressure tothe first and second substrates W1, W2, thus bonding the substrates W1,W2 together.

The pressing mechanism 36 c is formed like a gate. The pressingmechanism 36 c includes a support frame 121, a motor 125, a pair oflinear rails 122 a, 122 b, and a pair of linear guides 123 a, 123 b. Thesupport frame 121 is fixed at a predetermined position. The motor 125 issecured to the top of the support frame 121, as viewed in the drawing.The linear rails 122 a, 122 b are attached to the support frame 121 andoppose each other. The linear rails 122 a, 122 b movably support thelinear guides 123 a, 123 b, respectively. Upper and lower plates 124 a,124 b are held between the linear guides 123 a, 123 b. The upper andlower plates 124 a, 124 b and the linear guides 123 a, 123 b form asupport. A support arm 126 suspends the upper plate 124 a. The motor 125selectively lifts and lowers the support arm 126.

More specifically, a ball spring 127 is connected to the output shaft ofthe motor 125 and rotates integrally with the motor 125. The ball spring127 is fastened to a threaded portion 128 that is formed in a top plate126 a of the support arm 126. The ball spring 127 thus rotates toselectively lift and lower the support arm 126 depending on thedirection in which the motor 125 rotates.

The support arm 126 includes the top plate 126 a, a bottom plate 126 b,and a connecting plate 126 c. The top plate 126 a and the bottom plate126 b are parallel with each other. The connecting plate 126 c connectsthe top plate 126 a to the bottom plate 126 b. A plurality of load cells129 are attached to the upper side of the bottom plate 126 b and abutthe lower side of the upper plate 124 a, as viewed in FIG. 19.

The upper chuck unit 72 a is suspended from the lower side of the lowerplate 124 b. More specifically, a plurality of (four) holes are formedin the lower plate 124 b, and each hole receives a support post 130. Thelower plate 124 b includes a plurality of level adjusting portions 131at positions corresponding to the holes. As shown in FIG. 20, the upperchuck unit 72 a is attached to the distal ends, or the lower ends, ofthe support posts 130. The diameter of the upper end of each supportpost 130 is larger than that of the lower end such that the support post130 does not fall from the lower plate 124 b. Each level adjustingportion 131 is located between the upper end of the associated supportpost 130 and the lower plate 124 b.

It is preferred that each level adjusting portion 131 is a nut thatengages with a threaded portion of the associated support post 130. Eachlevel adjusting portion 131 rotates to selectively lift and lower theassociated support post 130, thus adjusting the horizontal level of theupper chuck unit 72 a. In this manner, the level adjusting portions 131adjusts the parallel level between the lower chuck unit 72 b and theupper chuck unit 72 a to 50 micrometers or smaller.

A pressing cylinder 132 is attached to the bottom plate 126 b of thesupport arm 126 and supplies pressure to the upper chuck unit 72 a. Itis preferred that a pressing cylinder 132 is an air pressure cylinder. Apressing piston 133 projects downward from the pressing cylinder 132,and the distal end of the pressing piston 133 abuts against a pressingmember 135 through a cylindrical coupling 134. The pressing member 135is attached to the upper chuck unit 72 a. If the axis of the pressingcylinder 132 is located offset from the center of the upper chuck unit72 a, the coupling 134 cancels the offset amount.

Each load cell 129 measures the pressure from the upper plate 124 a. Ifthe first and second substrates W1, W2 are not pressed to each other,the pressure is determined as the sum of the total weight A1 of thecomponents supported by the support arm 126 (the upper plate 124 a, thelinear guides 123 a, 123 b, the lower plate 124 b, the support posts130, the upper chuck unit 72 a, and the pressing cylinder 132), thepressure A2 applied by the pressing cylinder 132 to the upper chuck unit72 a, and the atmospheric pressure A3, or (A1+A2+A3). The measurement ofeach load cell 129 is supplied to a load indicator 136.

When the vacuum chamber 71 is depressurized, the atmospheric pressure ofabout 1 kg/cm² acts on the upper chuck unit 72 a through the supportposts 130. The atmospheric pressure acts on each load cell 129 throughthe lower plate 124 b, the linear guides 123 a, 123 b, and the upperplate 124 a. If the motor 125 is driven to lower the support arm 126 forbonding the first substrate W1 to the second substrate W2, or if thesubstrates W1, W2 are pressed to each other, the measurement of eachload cell 129 decreases by an amount corresponding to the reactive forceD of the first and second substrates W1, W2 (=A1+A2+A3−D). Accordingly,the load (pressure) that actually acts on each substrate W1, W2 isdetermined in accordance with the measurement of each load cell 129.

The load indicator 136 supplies the load controller 137 with themeasurement of each load cell 129. The load controller 137 is connectedto an electro-pneumatic pressure regulator 138. The load controller 137computes the pressure that acts on the first and second substrates W1,W2 (either is not shown in FIG. 19) based on the measurement of eachload cell 129, when the substrates W1, W2 are pressed to each otherbetween the upper and lower chuck units 72 a, 72 b. In accordance withthe computation, the load controller 137 sends a correction signal tothe electro-pneumatic pressure regulator 138 such that a constantpressure acts on the first and second substrates W1, W2. It is preferredthat the electro-pneumatic pressure regulator 138 is a variable pressureregulator. The electro-pneumatic pressure regulator 138 thus varies theair pressure supplied to the pressing cylinder 132 in accordance withthe correction signal from the load controller 137. In this manner, aconstant pressure acts on the first and second substrates W1, W2 thatare located between the upper and lower chuck units 72 a, 72 b. Thefirst and second substrates W1, W2 are thus bonded together through theconstant pressure.

Further, external factors such as the parallel level between the upperand lower chuck units 72 a, 72 b, a foreign object trapped in thepressing device 36, and offset installation of mechanical componentsreduce the pressure that acts on each load cell 129, in the same manneras the reactive force D. Accordingly, the load that actually acts on thefirst and second substrates W1, W2 is constantly measured based on adecrease in the measurement of each load cell 129. The load controller137 supplies the electro-pneumatic pressure regulator 138 with thecorrection signal in accordance with the measurement of each load cell129 such that the constant pressure acts on the upper and lower chuckunits 72 a, 72 b, regardless of the external factors.

The load controller 137 sends a movement signal to a motor pulsegenerator 139 to selectively raise and lower the upper chuck unit 72 a.The motor pulse generator 139 generates a pulse signal in accordancewith the movement signal and sends the pulse signal to the motor 125,thus actuating the motor 125 in accordance with the pulse signal.

Although the pressing cylinder 132 applies pressure to the first andsecond substrates W1, W2 in the illustrated embodiment, an actuator suchas a motor may replace the pressing cylinder 132. Further, the pressingcylinder 132 may be operated in accordance with hydraulic pressureinstead of air pressure.

Further, the position of the lower chuck unit 72 b may be adjustedinstead of that of the upper chuck unit 72 a to vary the parallel levelbetween the upper chuck unit 72 a and the lower chuck unit 72 b.

In addition, the pressing cylinder 132 or other pressure devices may beomitted as long as the total weight of the components held by thesupport arm 126 generates a sufficient pressure for pressing the firstand second substrates W1, W2 to each other. In this case, each load cell129 receives the total weight A1 of the upper chuck unit 72 a and thecomponents that support the upper chuck unit 72 a and the atmosphericpressure A3 that acts on the upper chuck unit 72 a when the vacuumchamber 71 is depressurized. Thus, if the first and second substratesW1, W2 are pressed to each other, the measurement of each load cell 129decreases by an amount that corresponds to the reactive force D of thesubstrates W1, W2. Accordingly, the load controller 137 determines thepressure that actually acts on the first and second substrates W1, W2based on the measurement of each load cell 129 (=A1+A3−D).

FIG. 21 is a view schematically showing the transport device 38 c thattransports the first and second substrates W1, W2 from the pressingdevice 36 to the hardening device 37 of FIG. 5. The lower part of FIG.21 indicates a procedure of the main controller 31 for controlling thealignment of the first and second substrates W1, W2. The transportdevice 38 c includes a transfer arm 141, a plurality of transport trays142 a, 142 b, . . . 142 z, and a lift 143.

The transfer arm 141 electrostatically attracts the bonded substratesW1, W2, or a panel display P1, from the lower chuck unit 72 b andtransports the panel display P1 to the exterior of the vacuum chamber71. The transfer arm 141 does not necessarily have to be anelectrostatic attraction type but may scoop the panel display P1 fromthe lift pins 73 that lift the panel display P1 separately from thelower chuck unit 72 b. Further, if the upper chuck unit 72 a holds thepanel display P1, the transfer arm 141 receives the panel display P1from the upper chuck unit 72 a.

Each transport tray 142 a-142 z is attached to the lift 143 one at atime. The lift 143 lifts the corresponding transport tray 142 a-142 z toa receiving position at which the transfer arm 141 places the paneldisplay P1 on the transport tray 142 a-142 z.

Each transport tray 142 a-142 z includes a flat plate 144 a and a vacuumholding mechanism 144 b that is secured to the lower side of the flatplate 144 a, as viewed in FIG. 21. In the drawing, only the flat plate144 a of the transport tray 142 z is given the reference index.

The upper side of each flat plate 144 a is machined to a flatness of 100micrometers or smaller. As shown in FIGS. 12C and 12D, a plurality ofattraction holes 145 is formed in each flat plate 144 a. The vacuumholding mechanism 144 b attracts the panel display P1 to the flat plate144 a through vacuum. The vacuum holding mechanism 144 b has a checkvalve. More specifically, when one transport tray 142 a-142 z isattached to the lift 143, the attraction holes 145 are connected to anair discharge device such as a vacuum pump (not shown). The airdischarge device thus attracts the panel display P1 to the correspondingtransport tray 142 a-142 z through vacuum. After the transport tray 142a-142 z is detached from the lift 143, the check valve prevents air fromflowing in an inverse direction. Accordingly, the panel display P1 isheld as attracted to the upper side of the flat plate 144 a.

It is preferred that each attraction hole 145 is a round hole with adiameter of two millimeters or smaller. The attraction holes 145suppress deformation (waviness) of the panel display P1, like thegrooves 89 of the upper and lower chuck units 72 a, 72 b.

The panel display P1 is transported to the hardening device 37 as heldon the corresponding transport tray 142 a-142 z. More specifically, whenbonding of one first substrate W1 with the corresponding secondsubstrate W2 is completed, the main controller 31 starts to measure thetime for each panel display P1, or the corresponding transport tray 142a-142 z. After a predetermined waiting period, the main controller 31permits each transport tray 142 a-142 z to transport the correspondingpanel display P1 to the hardening device 37.

Even after the first and second substrates W1, W2 are bonded together,reactive force remains acting on the bonded substrates W1, W2, or eachpanel display P1. The force is gradually released while the seal of thepanel display P1 is being hardened. Accordingly, the release of theremaining reactive force from each panel display P1 is substantiallycontrolled through adjustment of the waiting period. In other words, thetransport device 38 c holds the transport trays 142 a-142 z at theirwaiting positions during the waiting period such that the reactive forceis substantially released from each panel display P1. As a result, bythe time the seal is completely hardened, the reactive force iscompletely released from the panel display P1. This suppresses a defectin the panel display P1.

If the waiting period is uniform for each transport tray 142 a-142 z,the amount of the reactive force released from each panel display P1 isuniform. This makes deformation level of each panel display P1 (thebonded substrates W1, W2) uniform. Accordingly, the panel displays P1are stably manufactured without variation, thus improving thereproducibility for manufacturing the panel displays P.

The hardening device 37 includes an UV lamp 146. The UV lamp 146irradiates light of a predetermined wavelength that includes awavelength at which the seal hardens. Further, it is preferred that thelight has a wavelength that suppresses adverse effects of the light onliquid crystal. Since the second substrate W2, or the CF substrate, islocated above the first substrate W1 of each panel display P1, the UVlamp 146 irradiates the light to each panel display P1 from above.During the irradiation, liquid crystal is not directly exposed to thelight. This prevents the liquid crystal from being damaged by the light.

After the seal is hardened, the transport device 38 d transports eachpanel display P1 from the hardening device 37 to the inspection device35 of FIG. 5. The inspection device 35 performs an alignment inspection.That is, the inspection device 35 inspects each panel display P1 todetect the misalignment amount between the first substrate W1 and thesecond substrate W2. The inspection device 35 informs the maincontroller 31 of the detection result.

The main controller 31 associates the detection result with eachtransport tray 142 a-142 z. In accordance with the detection result, themain controller 31 corrects the alignment of the first and secondsubstrates W1, W2 in the pressing device 36 in a feed-back manner. Morespecifically, since each flat plate 144 a has a different flatness, eachtransport tray 142 a-142 z causes a different amount of misalignmentbetween the corresponding substrates W1, W2. Before bonding thesubstrates W1, W2 together in the pressing device 36, the maincontroller 31 associates each panel display P1 with one transport tray142 a-142 z. Thus, the main controller 31 misaligns the substrates W1,W2 in the pressing device 36 by an amount corresponding to themisalignment amount of the associated transport tray 142 a-142 z. Thefirst and second substrates W1, W2 are then bonded together. Thiscompensates the misalignment amount for each transport tray 142 a-142 a.

More specifically, as shown in FIG. 21, the main controller 31 stores amisalignment table 147 that includes data associated with each transporttray 142 a-142 z. For example, the misalignment table 147 includes thedata associated with the transport tray 142 a (X: +1, Y: −1). Thus,regarding the first and second substrates W1, W2 carried by thetransport tray 142 a, the main controller 31 selects the data (X: +1, Y:−1) as a correction amount from the misalignment table 147. The maincontroller 31 then moves each substrate W1, W2 in accordance with thecorrection amount for aligning the first and second substrates W1, W2.That is, the main controller 31 controls the alignment of the first andsecond substrates W1, W2 in accordance with the detection result of theinspection device 35 in a feedback manner. This suppresses misalignmentbetween the first and second substrates W1, W2 in each panel display P1.

The hardening device 37 will hereafter be described with reference toFIG. 22. The hardening device 37 includes a light source 148, anilluminometer 149, the irradiation controller 150, and a light sourcelift 151. The light source 148 includes the UV lamp 146 and first andsecond reflection plates 152, 153. Each reflection plate 152, 153reflects the light of the UV lamp 146 on the entire panel display P1 ina substantially uniform manner. In this manner, the light source 148exposes the entire panel display P1 to a substantially uniform energywhile preventing liquid crystal from being damaged by the light. If thelight source 148 does not have the first reflection plate 152, thecenter of the panel display P1 could be exposed to a more intense lightthan the periphery of the panel display P1. It is thus preferred thatthe light source 148 includes the first and second reflection plates152, 153.

The light lift 151 supports each transport tray 142 a-142 z. Eachtransport tray 142 a-142 z includes an irradiation sensor 154. Eachirradiation sensor 154 supplies the illuminometer 149 with anirradiation signal that has a value (for example, a voltage)representing the intensity of irradiation to which the correspondingpanel display P1 is exposed.

Based on the irradiation signal, the illuminometer 149 informs theirradiation controller 150 of the intensity of irradiation to which eachpanel display P1 is exposed. The irradiation controller 150 generates acontrol signal in accordance with the information and sends the controlsignal to the light source lift 151. The control signal includes, forexample, a signal adjusted to make the intensity of irradiation uniformor a signal that varies the intensity of irradiation as time elapses.

In response to the control signal, the light source lift 151 varies theinterval between the transport tray 142 a and the light source 148, asshown in FIG. 22. It is thus possible to easily control the intensity ofirradiation to which each panel display P1 is exposed, even if theirradiation of the first light source 148 is varied (due to, forexample, aging of the UV lamp 146, replacement of the UV lamp 146, or achange in the reflection surface of each reflection plate 152, 153).Accordingly, the seal hardens uniformly, thus suppressing a defect ineach panel display P1.

A second light source 155 identical to the first light source 148 may belocated below the transport tray 142 a, as shown in FIG. 22. The secondlight source 155 irradiates light to the panel display P1 through thebottom of the transport tray 142 a, thus hardening the seal quickly.Further, in this case, it is preferred that the light source lift 151moves the second light source 155 relative to the transport tray 142 a.

The irradiation controller 150 may control the drive voltage and drivecurrent of the light source 148 (155) in accordance with the amount ofirradiation, such that the amount of irradiation becomes substantiallyuniform between the substrate W1 and the substrate W2. Further, anirradiation sensor 156 may be located on the transport tray 142 a. Theirradiation controller 150 thus controls the drive voltage and drivecurrent of the light source 148 (155) in accordance with the amount ofirradiation that is measured by the irradiation sensor 156. If this isthe case, insufficient hardening of the seal is suppressed even if theirradiating device deteriorates to decrease the intensity ofirradiation.

The illustrated embodiment has the following advantages.

(1) When the pressure in the vacuum chamber 71 is substantially at theatmospheric level, the upper and lower chuck units 72 a, 72 brespectively hold the first and second substrates W1, W2 through vacuum.If the vacuum chamber 71 is depressurized, each chuck unit 72 a, 72 battracts the associated substrate W1, W2 electrostatically. Morespecifically, if the vacuum chamber 71 is depressurized, the pressure ineach depressurization line 78 a, 78 b and the pressure in eachattraction line 77 a, 77 b (the pressure that attracts each substrateW1, W2 to the associated chuck unit 72 a, 72 b) are controlled to beequal to the pressure in the vacuum chamber 71. In this state, eachsubstrate W1, W2 is electrostatically held by the associated chuck unit72 a, 72 b and is prevented from falling from or moving relative to thechuck unit 72 a, 72 b. This suppresses misalignment between the firstand second substrates W1, W2.

(2) The attraction grooves 89 formed in the upper electrostatic chuck 76a suppress deformation (waviness) of the second substrate W2 when theupper electrostatic chuck 76 a attracts the second substrate W2.

(3) The upper electrostatic chuck 76 a attracts the second substrate W2when voltage is supplied to the electrodes 92 a-92 d in the dielectriclayers 91 a-91 d. Further, when the first conductive connector 94 a,which is connected to the dielectric layer 91 a, supplies pressure tothe dielectric layer 91 a, the second substrate W2 separates from theupper electrostatic chuck 76 a. It is thus easy to control theattraction and separation of the second substrate W2 with respect to theupper electrostatic chuck 76 a.

(4) The seal material includes a photo-curing adhesive. The intervalbetween the light source 148 and the first and second substrates W1, W2is adjusted in accordance with the intensity of irradiation to which theseal to be hardened is exposed. The seal thus hardens uniformly, thussuppressing a defect in the resulting product.

(5) The drip controller 53 includes the syringe 55 that presses theliquid crystal LC through the nozzle 57 and the temperature controller60 that controls the temperature of the liquid crystal LC. The dripcontroller 53 is thus capable of dripping a relatively small amount ofthe liquid crystal LC with a high accuracy without being affected by theambient temperature. Further, the liquid crystal LC is dripped withoutforming bubbles, and the drip amount of the liquid crystal LC ismaintained as constant.

(6) The image pickup device 111 is switched between the first and secondlenses 115, 116, which have different fields of view, in accordance withthe interval between the first and second substrates W1, W2. The firstand second substrates W1, W2 are thus aligned with a high accuracywithout being contacted by the alignment device 36 a.

(7) When the first and second substrates W1, W2 are pressed to eachother, the measurement of each load cell 129 does not include thereactive force of the first and second substrates W1, W2. That is, themeasurement of each load cell 129 reflects the load that actually actson the first and second substrates W1, W2. The load controller 137electrically controls the electro-pneumatic pressure regulator 138 inaccordance with the measurement of each load cell 129. In this manner, aconstant pressure acts on the first and second substrates W1, W2regardless of the external factors.

It should be apparent to those skilled in the art that the presentinvention may be embodied in many other specific forms without departingfrom the spirit or scope of the invention. Particularly, it should beunderstood that the invention may be embodied in the following forms.

Each of the upper and lower electrostatic chucks 76 a and 76 b, asanother holding device, can be changed to any known holding device, suchas a mechanically holding arm (not shown), for holding the associatedsubstrate W1 and W2.

To prevent the side of each substrate W1, W2 at which the components areformed (the component forming side) from being contaminated or damaged,the opposite side of the substrate W1, W2 may be attracted to theassociated chuck unit 72 a, 72 b, as shown in FIG. 24A. Further, eachtransfer arm 74 (see FIG. 10), which supports the first and secondsubstrates W1, W2, may include a holder 163 that holds a peripheralportion 162 around a component forming portion 161. In this case, thesecond substrate W2 tends to bend, as shown in FIG. 24B. If the secondsubstrate W2 is bent, the second substrate W2 may be located offset withrespect to the upper chuck unit 72 a or may not be sufficientlyattracted to the upper chuck unit 72 a. This causes, for example,misalignment between the first and second substrates W1, W2. To avoidthis, the pressing device 36 may include correction mechanisms 165 forcorrecting the shape of the second substrate W2, as shown in FIGS. 23Aand 23B.

Each correction mechanism 165 includes a holding pad 166, an arm 167that supports the holding pad 166, and an arm lift (not shown) thatselectively raises and lowers the arm 167. The correction mechanisms 165lift the middle of the second substrate W2. More specifically, when theupper chuck unit 72 a attracts the second substrate W2 through vacuum,the attraction controller 84 actuates the correction mechanisms 165 tocorrect the bent shape of the second substrate W2.

FIG. 25A shows the second substrate W2 in a bent state. Each correctionmechanism 165 corrects the bent shape of the second substrate W2, asshown in FIG. 25B. The upper chuck unit 72 a is then lowered to attractthe second substrate W2 through vacuum, as shown in FIG. 25C.Subsequently, as shown in FIG. 25D, the upper chuck unit 72 a is raisedand each correction mechanism 165 and the holder 163 are separated fromthe second substrate W2. As a result, as shown in FIG. 25E, the upperchuck unit 72 a attracts the second substrate W2 at an accurateposition. This increases the reproducibility for attracting the secondsubstrate W2 to the upper chuck unit 72 a.

Although each correction mechanism 165 of FIGS. 23 and 24 includes theholding pad 166, the correction mechanism 165 may be configured in anyother manner as long as the bent shape of the second substrate W2 iscorrected. For example, the correction mechanisms 165 may correct thebent shape of the second substrate W2 without contacting the secondsubstrate W2. In either case, the correction mechanisms 165 have thesame advantage.

As shown in FIG. 26, a transport table 171 may replace the transportrobot 45 of FIG. 10. The transport table 171 transports the first andsecond substrates W1, W2 together and includes an upper holder 172 and alower holder 173. The upper holder 172 holds the second substrate W2such that the bonding side (the components forming side) faces downward.The lower holder 173 holds the first substrate W1 such that the bondingside faces upward. The upper holder 172 holds the second substrate W2 ata position outward from the seal applied on the first substrate W1. Theupper chuck unit 72 a attracts the second substrate W2 from the upperholder 172. The lower holder 173 places the first substrate W1 on thedistal ends of the lift pins 73. The lift pins 73 then allows the lowerchuck unit 72 b to attract the first substrate W1.

The transport table 171 aligns the first and second substrates W1, W2before placing the substrates W1, W2 in the vacuum chamber 71. Thetransport table 171 thus transports the first and second substrates W1,W2 together as held in an aligned state. This shortens the time neededfor alignment of the first and second substrates W1, W2 in the pressingdevice 36.

An alignment device 36 b, as shown in FIG. 27, may be employed. In thiscase, it is preferred that the lower chuck unit 72 b is detachable fromthe movement mechanism 113. Further, the movement mechanism 113 includesa base stage 175 and a plurality of alignment pins 176. The base stage175 supports the lower chuck unit 72 b, or a chuck portion. Thealignment pins 176 project from the base stage 175, and matchingalignment holes 177 are formed in the lower chuck unit 72 b. When eachalignment pin 176 is fitted in the associated alignment hole 177, thelower chuck unit 72 b is stopped from moving horizontally with respectto the base stage 175.

After the first and second substrates W1, W2 are bonded together, thesubstrates W1, W2 are maintained as held on the lower chuck unit 72 b.The lower chuck unit 72 b is then detached from the movement mechanism113. The transport device 38 c of FIG. 5 thus transports the substratesW1, W2 together with the lower chuck unit 72 b to the hardening device37. It is thus unnecessary to transfer the first and second substratesW1, W2 from the transport device 38 c to the corresponding transporttray 142 a-142 z. This reduces the number of the manufacturing steps,and the panel display P1 is manufactured in a further stable manner.

As shown in FIGS. 28A, 28B, 28C, a plurality of discharge grooves 178may be formed in the attraction side of the upper electrostatic chuck 76a, in addition to the attraction grooves 89. The discharge grooves 178equilibrate the pressure that acts on a portion of the attraction sideof the upper electrostatic chuck 76 a around the second substrate W2with the pressure in the vacuum chamber 71.

Each discharge groove 178 extends in a longitudinal direction of eachattraction groove 89. An end of each discharge groove 178 is located ina portion of the attraction side of the upper electrostatic chuck 76 athat attracts the second substrate W2. The other end of each dischargegroove 178 corresponds to an end of the upper electrostatic chuck 76 a.The discharge grooves 178 thus discharges air trapped between theperiphery of the second substrate W2 and the corresponding portion ofthe attraction side of the upper electrostatic chuck 76 a. This preventsthe second substrate W2 from moving relative to or falling from theupper electrostatic chuck 76 a.

The discharge grooves 178 reduce the contact area between the secondsubstrate W2 and the upper electrostatic chuck 76 a. This furthersuppresses misalignment between the first and second substrates W1, W2when the substrates W1, W2 are bonded together.

Alternatively, the discharge grooves 178 may be formed in the attractionside of the lower electrostatic chuck 76 b. This structure prevents thefirst substrate W1 from moving relative to or falling from the lowerelectrostatic chuck 76 b.

Each discharge groove 178 does not necessarily have to reach the end ofthe attraction side of the upper electrostatic chuck 76 a, as long asthe discharge groove 178 connects the portion of the attraction side ofthe upper electrostatic chuck 76 a that contacts the periphery of thesecond substrate W2 to the portion of the attraction side of theelectrostatic chuck 76 a around the second substrate W2.

If necessary, each substrate W1, W2 may be aligned by a pre-alignmentdevice before the substrates W1, W2 are transported to the pressingdevice 36 (for example, before the liquid crystal LC is dripped on thefirst substrate W1). The pre-alignment device includes a camera and astage. The stage carries each substrate W1, W2 and moves along the axisX (perpendicular to the transport direction of each substrate W1, W2)and rotates in a direction θ. It is preferred that the lens power of thecamera is lower than that of the first camera lens 115 (FIG. 17). Thatis, the bonded substrate manufacturing apparatus with the pre-alignmentdevice includes at least two pairs of lenses that have a power lowerthan that of the second camera lens 116 (FIG. 17).

The pre-alignment device stores a reference image and compares an imageof each substrate W1, W2 acquired by the camera with the referenceimage. The pre-alignment device thus detects misalignment between eachsubstrate W1, W2 and the reference image along the axes X and Y and inthe direction θ (misalignment amounts X, Y, and θ). The pre-alignmentdevice moves the stage to correct the position of each substrate W1, W2in accordance with the misalignment amounts X and θ. The pre-alignmentdevice informs the transport device 38 b of FIG. 5 of the misalignmentamount Y. The transport device 38 b corrects the position of the firstand second substrates W1, W2 in accordance with the misalignment amountY. That is, the transport device 38 b corrects the misalignment betweenthe first and second substrates W1, W2 along the axis Y whiletransporting the substrates W1, W2 to the pressing device 36, thussaving time. This increases the manufacturing efficiency of the paneldisplay P1.

The reference image of the pre-alignment device is obtained as follows.When the apparatus 30 of FIG. 5 is assembled, the drip device 33 and thepressing device 36 are located slightly offset. The apparatus 30 is thusinitially operated to detect the offset amount of the devices 32, 35.

More specifically, the upper section of FIG. 29 indicates a targetposition 181 for each substrate W1, W2 in the pressing device 36, atarget position 182 for each substrate W1, W2 in the drip device 33, andthe target position 183 for each substrate W1, W2 in the pre-alignmentdevice. To locate each substrate W1, W2 at the target position 181 inthe pressing device 36, the substrate W1, W2 must be located at thetarget position 183 in the pre-alignment device and the target position182 in the drip device 33. In other words, if each substrate W1, W2 islocated at the target position 183 in the pre-alignment device, thesubstrate W1, W2 is eventually located at the target position 181 in thepressing device 36. Thus, the pre-alignment device acquires an image ofeach substrate W1, W2 located at the target position 183 and stores theimage as the reference image.

The lower section of FIG. 29 indicates a transport path of eachsubstrate W1, W2 from the pre-alignment device to the pressing device36. More specifically, when the pre-alignment device receives eachsubstrate W1, W2, the center of the substrate W1, W2 is located offsetfrom that of the reference position 183. The pre-alignment device thuscompares a camera image of each substrate W1, W2 with the referenceimage and determines the misalignment amounts X, Y, and θ. Thepre-alignment device then moves the stage to correct the position ofeach substrate W1, W2 in accordance with the misalignment amounts X andθ. The pre-alignment device informs the transport device 38 b of themisalignment amount Y as a correction value. When the drip device 33receives each substrate W1, W2 from the transport device 38 a, thesubstrate W1, W2 is located substantially at the target position 182.The transport device 38 b then moves the first and second substrates W1,W2 from the drip device 33 toward the pressing device 36 by a distancethat corresponds to the total of the interval between the drip device 33and the pressing device 36 and the correction value. Accordingly, by thetime the pressing device 36 receives each substrate W1, W2, themisalignment amount Y is corrected. As a result, the first and secondsubstrates W1, W2 are located substantially at the target position 181when received by the pressing device 36.

As described, the pre-alignment device and the transport device 38 bsave time by correcting the misalignment amount Y of each substrate W1,W2 when the substrates W1, W2 are being transported from the drip device33 to the pressing device 36. Further, when the pressing device 36receives the first and second substrates W1, W2, each substrate W1, W2is located substantially at the target position 181. The alignment ofthe first and second substrates W1, W2 in the pressing device 36 is thusquickly completed.

Further, the pre-alignment device aligns the first and second substratesW1, W2 through a camera image of the substrates W1, W2 withoutcontacting the substrates W1, W2. This suppresses dust formationotherwise caused by contact between a rough surface of each substrateW1, W2 and the pre-alignment device.

The pre-alignment device stores the reference image during theinitialization when the bonded substrate manufacturing apparatus 30 isassembled. This compensates an assembly error of the apparatus 30. It isthus easy to provide an additional treatment device to the apparatus 30.

The present invention may be applied to, for example, a plasma paneldisplay (PDP), an electro-luminescence display (EL display), or anorganic display, instead of a liquid crystal display.

When bonding the first and second substrates W1, W2 in the pressingdevice 36, the upper chuck unit 72 a may be used as a referenceposition, instead of the lower chuck unit 72 b.

A heater that thermally hardens the seal may replace the UV lamp 146 ofthe hardening device 37.

The transport trays 142 a-142 z of FIG. 21 may be transported togetherwith the lift 143.

To prevent each substrate W1, W2 from falling from or moving relative tothe associated chuck unit 72 a, 72 b in the vacuum chamber 71 of FIG.11, the pressure for attracting the substrate W1, W2 needs be lower thanthe pressure in the vacuum chamber 71. Accordingly, the pressureequilibration valves 82 a, 82 b may be omitted. In this case, theattraction controller 84 opens the depressurization valves 80 a, 80 bwhen depressurizing the vacuum chamber 71. This structure also preventseach substrate W1, W2 from falling from or moving relative to theassociated chuck unit 72 a, 72 b in the vacuum chamber 71.

As in a bonded substrate manufacturing apparatus 201 of FIG. 30, somesteps other than the pressing step may be performed underdepressurization. The apparatus 201 includes a seal applying device 32,a carrying-in robot 202, a first vacuum sub-chamber 203, a bondingchamber 204, a second vacuum sub-chamber 205, a carrying-out robot 206,an inspection device 35, and a main controller 207.

A first gate valve 211 is located in the first vacuum sub-chamber 203for receiving the first and second substrates W1, W2. A second gatevalve 212 separates the first vacuum sub-chamber 203 from the bondingchamber 204. A third gate valve 213 separates the bonding chamber 204and the second vacuum sub-chamber 205. The substrates W1, W2 are bondedtogether in the bonding chamber 204. A fourth gate valve 214 is locatedin the second vacuum sub-chamber 205. The bonded substrates W1, W2, or apanel, exit the second vacuum sub-chamber 205 through the fourth gatevalve 214.

The main controller 207 controls the operation of each gate valve211-214, the pressure in each vacuum sub-chamber 203, 205, the pressurein the bonding chamber 204, the operation of the carrying-in robot 202,and the operation of the carrying-out robot 206. The seal applyingdevice 32 applies seal on the upper side of the first substrate W1. Theseal is not applied on any side of the second substrate W2. Thecarrying-in robot 202 transports the first and second substrates W1, W2to the first vacuum sub-chamber 203. The main controller 207 thenpretreats the substrates W1, W2 in the first vacuum sub-chamber 203. Inthe pretreatment, impurities adhered to the surfaces of each substrateW1, W2, or a display element, are exposed to reaction gas andreplacement gas for a predetermined time. The reaction gas is, forexample, exciting gas for plasma panel displays. The replacement gas is,for example, inactive gas such as nitrogen gas.

A pretreatment device that performs at least one of heating, plasmatreatment, and the aforementioned gas treatment may be located in thefirst vacuum sub-chamber 203. If the heating is performed, thesubstrates W1, W2 are heated to alter the surface quality of eachsubstrate W1, W2, activate the bonding surface of each substrate W1, W2,and remove water from the substrates W1, W2. If the plasma treatment isperformed, the impurities and substances that cannot be activatedthrough the reaction gas or the replacement gas or the heating areremoved using plasma.

The pretreatment stabilizes the quality of the bonding surfaces of thesubstrates W1, W2, which cannot be separated once they are bondedtogether. More specifically, an oxide film formed on each substrate W1,W2 or a foreign object adhered to the substrate W1, W2 alters thesurface state of the substrate W1, W2. The alteration is non-uniformamong the substrates W1, W2, thus hampering stable fabrication of paneldisplays. However, the pretreatment suppresses formation of the oxidefilm and adhesion of the foreign object and removes impurities from thesubstrates W1, W2. This maintains the surface of each substrate W1, W2in a certain state and stabilizes the quality of a product. Asdescribed, since the bonded substrate manufacturing apparatus 201 doesnot require a separate pretreatment device, the productivity formanufacturing bonded substrates is improved.

To prevent the plasma treatment from adversely affecting the seal on thefirst substrate W1, it is preferred that the seal is masked or thatplasma is generated in the portions other than the seal.

When fabricating a liquid crystal panel display, the liquid crystal dripdevice 33 of FIG. 5 may be located in the first vacuum sub-chamber 203.

After the pretreatment, the first and second substrates W1, W2 aretransported from the first vacuum sub-chamber 203 to the bonding chamber204. The pressing device 36 of FIG. 5 is located in the bonding chamber204. The pressing device 36 includes the alignment device 36 a of FIG.17 (or the alignment device 36 b of FIG. 27).

The main controller 207 controls the pressure in the bonding chamber 204and supply of the aforementioned gases. Further, the main controller 207aligns the first and second substrates W1, W2 and bonds the substratesW1, W2 together. More specifically, the main controller 207 measures thetime that elapses after the bonding chamber 204 receives the substratesW1, W2, thus controlling the time for which the substrates W1, W2 areexposed to the gases. This stabilizes the quality of the bonding surfaceof each substrate W1, W2. The bonded substrates W1, W2, or a panel, aretransported from the bonding chamber 204 to the second vacuumsub-chamber 205.

The transport device 38 c and the hardening device 37 of FIG. 5 arelocated in the second vacuum sub-chamber 205. After depressurizing thesecond vacuum sub-chamber 205, the main controller 207 transports thefirst and second substrates W1, W2 to the second vacuum sub-chamber 205.The main controller then operates the hardening device 37 to harden theseal in the second vacuum sub-chamber 205. Since the seal is hardenedunder depressurization, the substrates W1, W2 are prevented frombecoming offset from each other when the pressure is restored.

The first vacuum sub-chamber 203 or the second vacuum sub-chamber 205may be canceled.

Alternatively, a plurality of first vacuum sub-chambers 203 may beprovided in parallel. In this case, a plurality of pairs of first andsecond substrates W1, W2 are pretreated in the first vacuum sub-chambers203. Afterwards, each pair of first and second substrates W1, W2 isbonded together in the bonding chamber 204, one pair at a time. Thisreduces the manufacturing time per one bonded substrate, or one pair offirst and second substrates W1, W2.

The alignment device 36 a of FIG. 17 may perform the correction of theimage pickup device 111 as follows. That is, the alignment device 36 astores the positions (within the field of view) of the alignment marksused for aligning the first and second substrates W1, W2. When receivingthe substrates W1, W2, the alignment device 36 a horizontally moves theimage pickup device 111 in accordance with the difference (thecoordinate difference) between the actual position of the alignment markof each substrate W1, W2 and the stored positions.

More specifically, as shown in FIG. 31A, a reference substrate that hasan alignment mark M0 is transported to the alignment device 36 a, afterthe position of the reference substrate is corrected by the method shownin FIG. 29. Thus, even if the position of the reference substratebecomes offset during the transportation, the alignment mark M0 of thereference substrate is located within the field of view F1 of the firstcamera lens 115 (FIG. 31A). Further, when the image pickup device 111 ismoved by a predetermined distance to acquire an image of the referencesubstrate with the second camera lens 116, the alignment mark M0 of thereference substrate is located within the field of view of the secondcamera lens 116. The alignment controller 114 of FIG. 17 stores theposition (coordinates X, Y) of the alignment mark M0 in the field ofview F1 of the first camera lens 115.

Subsequently, the first substrate W1 is transported to the alignmentdevice 36 a. The first camera lens 115 of the alignment device 36 aacquires an image of the alignment mark M1 of the first substrate W1. InFIG. 31B, the alignment mark M1 is located in the field of view F2 ofthe first camera lens 115. The alignment controller 114 computes theposition (coordinates x, y) of the alignment mark M1 in the field ofview F2. The alignment controller 114 moves the first camera lens 115 inaccordance with the difference between the computed coordinates (x, y)and the stored coordinates (X, Y) such that the position of thealignment mark M1 corresponds to the position of the alignment mark M0in a corrected field of view F2 a (FIG. 31C). Accordingly, when thefirst camera lens 115 is switched to the second camera lens 116, thealignment mark M1 is reliably located in the field of view of the secondcamera lens 116.

Further, the movement amount of the image pickup device 111 forswitching the first camera lens 115 to the second camera lens 116 may becorrected in accordance with the difference between the computedcoordinates (x, y) and the stored coordinates (X, Y).

In addition, the above operation, which includes the storing of thepositions of the alignment marks M0, M1 in the field of view, may beapplied to a substrate W3 that has a large alignment mark Ma and a smallalignment mark Mb. The first camera lens 115, which has a relativelysmall power, acquires an image of the large alignment mark Ma. Thesecond camera lens 116, which has a relatively large power, acquires animage of the small alignment mark Mb. For example, as shown in FIG. 32,four large alignment marks Ma, each of which is paired with one smallalignment mark Mb, are located at predetermined positions (four corners)of the substrate W3. Each large alignment mark Ma is spaced from thecorresponding small alignment mark Mb at a predetermined interval.Further, a substrate to be aligned with the substrate W3 (for example,the second substrate W2, if the large alignment marks Ma and the smallalignment marks Mb are located in the first substrate W1) includes aplurality of alignment marks (not shown) that correspond to the largealignment marks Ma and the small alignment marks Mb of the substrate W3.

As shown in FIG. 33A, the axis of the first camera lens 115 and the axisof the second camera lens 116 are spaced from each other at an uniforminterval. FIG. 33B is an image of one large alignment mark Ma acquiredby the first camera lens 115 when the large alignment mark Ma is locatedat an optimal position. FIG. 33C is an image of one small alignment markMb acquired by the second camera lens 116 when the small alignment markMb is located at an optimal position. The alignment controller 114stores the images of FIGS. 33B, 33C and the position of the image pickupdevice 111 corresponding to the image of FIG. 33B relative to theposition of the image pickup device 111 corresponding to the image ofFIG. 33C.

FIG. 33D is an image of one large alignment mark Ma of the substrate W3acquired by the first camera lens 115 when the substrate W3 istransported to the alignment device 36 a of FIG. 17. The alignmentcontroller 114 computes the movement amount and movement angle (X, Y,and θ) of the image pickup device 111 for locating the large alignmentmark Ma at the position corresponding to the stored image of FIG. 33B.The alignment controller 114 moves the image pickup device 111 inaccordance with the computed movement amount and movement angle.

Subsequently, the alignment controller 114 moves the image pickup device111 by a certain amount to switch from the first camera lens 115 to thesecond camera lens 116. This movement amount is equal to the intervalbetween the position of the image pickup device 111 corresponding to theimage of FIG. 33B and the position of the image pickup device 111corresponding to the image of FIG. 33C. Thus, as long as the substrateW3 remains unmoved, the offset amount of the small alignment mark Mb inthe field of view of the second camera lens 116 can be predicted fromthe position of the large alignment mark Ma in the field of view of thefirst camera lens 115.

In this manner, the alignment marks are reliably located in the field ofview of each camera lens 115, 116. Accordingly, when the substratebonding is performed, the second camera lens 116 reliably acquires thesmall alignment mark Mb in its field of view, as shown in FIG. 33E. As aresult, the substrate alignment is achieved further precisely.

The movement amount of the image pickup device 111 is controlled using apulse. Further, the first and second camera lenses 115, 116 may beattached to separate cameras. If this is the case, the interval betweenthe cameras (the optical axes of the camera lenses 115, 116) must befixed.

The numbers, the positions, or the shapes of the large or smallalignment marks Ma, Mb may be modified as necessary. For example, asshown in FIG. 32, a pair of large alignment marks Ma may be located at apair of positions (near the middle of the upper side and near the middleof the lower side) of the substrate W3. Further, each alignment mark,Ma, Mb, M0, M1, M2 may be shaped as a square or a cross. In addition,the alignment marks of one substrate may have different shapes, thusmaking it easy to determine the orientation of the substrate.

The pre-alignment may be performed using the large alignment marks Mabefore the first and second substrates W1, W2 are transported to thepressing device 36. FIG. 34 shows a portion of the pressing device 36,or the alignment device 36 a. A pre-alignment device 221 pre-aligns thefirst and second substrates W1, W2 before the substrates W1, W2 aretransported to the pressing device 36, which includes the alignmentdevice 36 a of FIG. 17.

The pre-alignment device 221 includes an image pickup device 222, amovement mechanism 223, a controller 224, a chuck unit 225, and a stage(not shown). The movement mechanism 223 moves the image pickup device222. The controller 224 controls the movement mechanism 223. The chuckunit 225 holds a substrate W. The stage moves the chuck unit 225. Morespecifically, the stage horizontally moves the chuck unit 225 in thedirection X parallel with the transport direction and the direction Yperpendicular to the transport direction. Further, the stage rotates thechuck unit 225 in the direction 0. The image pickup device 222 includesa third camera lens 226 with a power smaller than that of the firstcamera lens 115. That is, for example, the power of the first cameralens 115 is ×6, that of the second camera lens 116 is ×10, and that ofthe third camera lens 226 is ×2. The third camera lens 226, the firstcamera lens 115, and the second camera lens 116 acquire images of onelarge alignment mark in fields of view F11, F12, F13, respectively, asshown in FIG. 34. The bonded substrate manufacturing apparatus with thepre-alignment device 221 includes the second camera lens 116 for precisealignment and at least two lenses that have lower powers than that ofthe second camera lens 116. Although not illustrated, a plurality ofpre-alignment devices 221 are located at positions at which eachpre-alignment device 221 can acquire an image of the corresponding largealignment mark Ma.

The controller 224 stores a reference image of the large alignment markMa acquired by the third camera lens 226. The reference image isobtained as follows. A reference substrate is positioned at an optimalposition in the alignment device 36 a. The reference substrate is thenreturned from the pressing device 36 to the pre-alignment device 221 asshown in FIG. 29. Subsequently, the pre-alignment device 221 acquires animage of the large alignment mark Ma of the reference substrate. Thecontroller 224 stores this image as the reference image.

Afterwards, the pre-alignment device 221 receives the first and secondsubstrates W1, W2 (only the first substrate W1 is shown in FIG. 34). Thepre-alignment device 221 then acquires an image of the substrate W1 withthe third camera lens 226 and compares the image with the referenceimage to measure the offset amount between the position of the firstsubstrate W1 and the reference position (X, Y, and θ). The offset amountis substantially equal to the relative coordinate position (the offsetamount) of the corresponding small alignment mark Mb of the substrate W1that is received by the pressing device 36 without being pre-aligned,the image of which is acquired by the second camera lens 116. That is,the pre-alignment device 221 predicts the offset amount of the substrateW1 that would otherwise be detected in the alignment device 36 a.

The pre-alignment device 221 moves the stage to compensate the offsetamount of the substrate W1. A transport device 227 then transports thesubstrate W1 to the lower holder 173 of the transport table 171.Similarly, the second substrate W2 is transported to the upper holder172 of the transport table 171. The transport table 171 then transportsthe first and second substrates W1, W2 to the pressing device 36. Sincethe substrates W1, W2 have been pre-aligned by the pre-alignment device221, the corresponding small alignment mark Mb of each substrate W1, W2is located substantially at the middle of the field of view (along theoptical axis) of the second camera lens 116 of the pressing device 36.This suppresses distortion of an image and reduces alignment errors. Thealignment thus becomes precise. Further, the second camera lens 116acquires the small alignment mark Mb in its field of view in arelatively short time. This shortens the time required for aligning thefirst and second substrates W1, W2 and bonding the substrates W1, W2together.

Alternatively, devices other than the chuck unit 225 may correct theposition of each substrate W (W1, W2). For example, as shown in FIG. 29,the transport device 227 may move the substrate W toward the transporttable 171 by a movement amount that compensates the offset amount (X) ofthe substrate W in the transport direction. Further, the transportdevice 227 may compensate the offset amount (θ) of the substrate W byreceiving the substrate W with an arm of the transport device 227inclined in accordance with the offset amount (θ) with respect to thetransport direction. In these cases, the first and second substrates W1,W2 are transported to the pressing device 36 such that the correspondinglarge alignment mark Ma is located in the field of view of the firstcamera lens 115 and the corresponding small alignment mark Mb is locatedin the field of view of the second camera lens 116.

Instead of moving the lower chuck unit 72 b of FIG. 19 by means of themovement mechanism 113, the chamber 71 and the lower chuck unit 72 b maybe moved together, thus aligning the first and second substrates W1, W2.For example, an alignment device 230 of FIG. 35 may be employed. Thealignment device 230 includes a vacuum chamber 231 and a movementmechanism 232. The vacuum chamber 231 has an upper section 231 a and alower section 231 b. The vacuum chamber 231 is connected to a pump 236through a pipe 233, a valve 234, and a pipe 235. The vacuum chamber 231is depressurized through the operation of the pump 236 and that of thevalve 234. An opening/closing mechanism (not shown) supports the uppersection 231 a with respect to the lower section 231 b to selectivelyopen and close the vacuum chamber 231. The movement mechanism 232rotationally supports the lower section 231 b and moves the lowersection 231 b in two directions along a hypothetical plane. The vacuumchamber 231 accommodates an upper chuck unit 237 a and a lower chuckunit 237 b. A fixed support plate 239 supports the upper chuck unit 237a through a plurality of support posts 238. A bellows 240 is locatedaround each support post 238 between the support plate 239 and the uppersection 231 a. The bellows 240 maintains the vacuum chamber 231 in anair-tight state. The lower chuck unit 237 b is secured to the bottom ofthe lower section 231 b.

An O-ring 241 and a temporary stop pin 242 are located between the uppersection 231 a and the lower section 231 b at positions where the upperand lower sections 231 a, 231 b contact each other. The O-ring 241 sealsthe space between the upper and lower sections 231 a, 231 b. When themovement mechanism 232 moves the lower section 231 b, the temporary stoppin 242 moves the upper section 231 a to follow the movement of thelower section 231 b.

In the alignment device 230, the vacuum chamber 231 in an open statereceives the first and second substrates W1, W2. The upper chuck unit237 a holds the second substrate W2, and the lower chuck unit 237 bholds the first substrate W1. After receiving the substrates W1, W2, thevacuum chamber 231 closes. The valve 234 and the pump 236 then operateto depressurize the vacuum chamber 231.

The vacuum chamber 231 in the depressurized state is moved to align thefirst and second substrates W1, W2 in the alignment device 230. Thisstructure requires a significantly less number of parts, as compared toprior art alignment devices 250, 260 respectively shown in FIGS. 36 and37. Further, the alignment device 230 advantageously suppresses particlegeneration from the O-ring 241. In addition, the temporary stop pin 242advantageously connects the upper and lower sections 231 a, 231 b toeach other with high accuracy. However, since the depressurization ofthe vacuum chamber 231 enables the upper and lower sections 231 a, 231 bto closely contact each other, the temporary pin 242 may be canceled.

FIG. 36 schematically shows a first prior art, or the alignment device250, and FIG. 37 schematically shows a second prior art, or thealignment device 260.

The first prior art alignment device 250 includes a vacuum chamber 251that has an upper section 251 a and a lower section 251 b. The lowersection 251 b is fixed, and the upper section 251 a is movably supportedby a movement mechanism (not shown). The vacuum chamber 251 is opened bymoving the upper section 251 a.

The vacuum chamber 251 accommodates an upper chuck unit 252 a and alower chuck unit 252 b. The upper chuck unit 252 a is secured to a fixedsupport plate 254 through a plurality of support posts 253. A bellows255 is located around each support post 253 between the support plate254 and the upper section 251 a. The bellows 255 maintains the vacuumchamber 251 in an air-tight state. The lower chuck unit 252 b isconnected to a support plate 257 through a plurality of support posts256. A movement mechanism (not shown) rotationally supports the supportplate 257 and moves the support plate 257 in two directions along ahypothetical horizontal plane. A bellows 258 is located around eachsupport post 256 between the support plate 257 and the lower section 251b. The bellows 258 maintains the vacuum chamber 251 in an air-tightstate. An O-ring 259 is located between the upper section 251 a and thelower section 251 b at a position where the upper and lower sections 251a, 251 b contact each other.

Accordingly, as compared to the first prior art alignment device 250 ofFIG. 36, the alignment device 230 of FIG. 35 requires a significantlyless number of parts, thus making it easy to maintain the alignmentdevice 230.

The second prior art alignment device 260 of FIG. 37 includes a vacuumchamber 261 that has an upper section 261 a and a lower section 261 b.The upper section 261 a is fixed, and the lower section 261 b isrotationally supported by a movement mechanism (not shown). Also, themovement mechanism moves the lower section 261 b in two directions alonga hypothetical horizontal plane. The upper section 261 a accommodates anupper chuck unit 262 a, and the lower section 261 b accommodates a lowerchuck unit 262 b. The upper and lower chuck units 262 a, 262 b arefixed. An O-ring 263 is located between the upper section 261 a and thelower section 261 b at a position where the upper and lower sections 261a, 261 b contact each other.

Accordingly, the alignment device 260 of FIG. 37 requires asignificantly less number of parts, as compared to the alignment device250 of FIG. 36. However, in the alignment device 260, the lower section261 b moves relative to the upper section 261 a for aligning the fistand second substrates W1, W2. This makes it difficult to maintain theperformance of the O-ring 263, which seals the space between the upperand lower sections 261 a, 261 b. Further, particles are generated fromthe O-ring 263 or the like when the lower section 261 b slides along theupper section 261 a. This is undesirable since the particles contaminatethe substrates W1, W2 before they are bonded together. In contrast, thealignment device 230 of FIG. 35 suppresses the particle generation andmakes it easy to maintain the O-ring 241. The alignment device 230 isthus preferred for a long-term operation.

A hardening device 270 of FIG. 38 may replace the hardening device 37 ofFIG. 22. The hardening device 270 includes a light source 271, acontroller 273, and a cooling mechanism 274. The light source 271 isidentical with the light source 148 of FIG. 22. Further, a second lightsource 276 identical with the light source 155 of FIG. 22 may be locatedbelow a chuck unit 275.

The chuck unit 275 supports the substrates W1, W2 that are bondedtogether, or a panel P1. The chuck unit 275 is configured to suppressreflection. That is, for example, the chuck unit 274 may be providedwith a black surface that absorbs light. Since reflection is suppressedon the chuck unit 275, the seal of the panel P1 hardens in asubstantially constant time. If reflection is not suppressed on thechuck unit 275, the seal of the panel P1 is exposed to both the lightfrom the light source 271 and the light reflected on the chuck unit 275.The seal thus hardens in a relatively short time as compared to the casein which the seal is exposed to only the light from the light source271. This makes it difficult to control the time for hardening the seal.

The cooling mechanism 274 maintains the temperature of the surface ofthe chuck unit 275 that faces the light source 271 at a predeterminedlevel such that the time for hardening the seal of the panel P1substantially remains in a certain range. More specifically, the seal ofthe panel P1 is hardened by the light from the light source 271. Thus,the surface of the chuck unit 275 that faces the light source 271 isheated by the light that passes through the panel P1, or the heattransmitted from the panel P1. Further, since the chuck unit 275suppresses reflection by, for example, absorbing light, the temperatureof the surface of the chuck unit 275 that faces the light source 271easily increases.

If the temperature of the surface of the chuck unit 275 that faces thelight source 271 increases, the heat from the chuck unit 275 starts toharden the seal of the panel P1 immediately after the panel P1 ismounted on the chuck unit 275. This makes it difficult to determine theonset of the seal hardening, and the seal hardening time cannot becontrolled. Further, if the light irradiation time for the chuck unit275 with a non-heated surface is applied to the chuck unit 275 with aheated surface, the heat may deteriorate or damage components of thepanel P1 such as liquid crystal, a driver IC, and a transistor.

The cooling mechanism 274 includes a temperature detecting mechanism 281and a surface cooling mechanism 282. The temperature detecting mechanism281 has a sensor 283 and the controller 273. The sensor 283 detects thetemperature of the surface of the chuck unit 275 and includes a sensorhead 284 and a thermometer 285. The sensor head 284 detects the surfacetemperature of the chuck unit 275 in a non-contact manner, thusoutputting a detection signal. The thermometer 285 converts the signalto temperature data. The controller 273 then compares the temperaturedata with pre-stored target temperature data.

The surface cooling mechanism 282 includes the controller 273, acompressor 286, a gas blower head 287, a gas drawer head 288, and a gasdrawer pump 289. The controller 273 controls the compressor 286 inrelation to a result from the aforementioned comparison. The gas blowerhead 287 is connected to the compressor 286. Accordingly, the gas blowerhead 287 blows gas toward the surface of the chuck unit 275, thuscooling the chuck unit 275. The gas drawer head 288 is connected to thegas drawer pump 289. The gas drawer pump 289 thus operates the gasdrawer head 288 to draw the gas blown from the gas blower head 287. Thisimproves the cooling efficiency.

The present examples and embodiments are to be considered asillustrative and not restrictive and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalence of the appended claims.

1. A liquid crystal drip device used in manufacture of a bondedsubstrate from a first substrate and a second substrate, the liquidcrystal drip device comprising: a dispenser including a discharge nozzleconfigured to drip a liquid crystal on at least either one of the firstand second substrates; a measurement device configured to measure a dripamount of the liquid crystal dripped from the dispenser; a dripcontroller configured to control the drip amount of the liquid crystaldripped on said at least either one of first and second substrates basedon a measurement result of the measurement device; an air blowerconfigured to generate an air flow directed toward the discharge nozzleto blow away the liquid crystal adhered to the discharge nozzle of thedispenser; and an air drawer configured to aspirate the air flow and theliquid crystal adhered to the discharge nozzle blown by the air blower;wherein the drip controller is coupled to the air blower and the airdrawer and is programmed to simultaneously operate the air drawer andthe air blower.
 2. The liquid crystal drip device according to claim 1,wherein the dispenser includes a plunger configured to pressurize theliquid crystal in the dispenser, wherein the drip controller controlsthe drip amount of the liquid crystal by driving the plunger.
 3. Theliquid crystal drip device according to claim 2, further comprising: amovement mechanism configured to support the dispenser and horizontallymove the dispenser.
 4. The liquid crystal drip device according to claim3, wherein the movement mechanism moves the dispenser to a locationwhere the liquid crystal is to be dripped.
 5. The liquid crystal dripdevice according to claim 1, wherein the measurement device is anelectronic balance.
 6. The liquid crystal drip device according to claim1, further comprising: a temperature controller configured to control atemperature of the liquid crystal in the dispenser.
 7. The liquidcrystal drip device according to claim 1, wherein the drip controller isprogrammed to actuate the air blower coupled to a compressor and the airdrawer coupled to a vacuum pump to clean a distal end of the dischargenozzle of the dispenser.
 8. A liquid crystal drip device used inmanufacture of a bonded substrate from a first substrate and a secondsubstrate, the liquid crystal drip device comprising: a dispenserconfigured to drip a liquid crystal on at least either one of the firstand second substrates; a measurement device configured to measure a dripamount of the liquid crystal dripped from the dispenser; a dripcontroller configured to control the drip amount of the liquid crystaldripped on said at least either one of first and second substrates basedon a measurement result of the measurement device; a syringe configuredto discharge the liquid crystal from the dispenser when pressurized,wherein the syringe includes a rotary valve body arranged in the syringeat a location between an upper section of the syringe and a nozzle ofthe syringe, the rotary valve body including a valve hole having a holediameter substantially equal to an inner diameter of the syringe, andthe rotary valve body is configured to open and close a liquid crystalpassage in the syringe at the location between the upper section and thenozzle to selectively block a movement of the liquid crystal.
 9. Theliquid crystal drip device according to claim 8, further comprising aliquid crystal supply structure configured to supply the liquid crystalto the dispenser.
 10. The liquid crystal drip device according to claim9, wherein the liquid crystal supply structure supplies the liquidcrystal to the syringe when the valve is repeatedly opened and closed.11. The liquid crystal drip device according to claim 8, furthercomprising: an air blower configured to generate an air flow to blowaway the liquid crystal adhered to a discharge nozzle of the dispenser;and an air drawer configured to aspirate the air flow and the liquidcrystal adhered to the discharge nozzle blown by the air blower.
 12. Theliquid crystal drip device according to claim 8, wherein the dispenserincludes a discharge nozzle and a plunger configured to pressurize theliquid crystal stored in the syringe, wherein the dispenser dischargesthe liquid crystal through the discharge nozzle by driving the plunger.13. The liquid crystal drip device according to claim 8, wherein themeasurement device is an electronic balance.
 14. The liquid crystal dripdevice according to claim 8, further comprising: a temperaturecontroller configured to control a temperature of the liquid crystal inthe dispenser.
 15. A liquid crystal drip device used in manufacture of abonded substrate from a first substrate and a second substrate, theliquid crystal drip device comprising a dispenser configured to drip aliquid crystal on at least either one of the first and secondsubstrates, wherein the dispenser includes: a syringe configured toretain the liquid crystal; a plunger configured to pressurize the liquidcrystal; a discharge nozzle through which the liquid crystal isdischarged; a rotary valve body arranged in the syringe at a locationbetween the plunger and the discharge nozzle, the rotary valve bodyincluding a valve hole having a hole diameter substantially equal to aninner diameter of the syringe, and wherein the rotary valve body isrotated to open and close a liquid crystal passage in the syringe at thelocation between the plunger and the discharge nozzle to control a flowof the liquid crystal between the plunger and the discharge nozzle; anda drip controller configured to control a drip amount of the liquidcrystal by controlling a displacement of the plunger.
 16. The liquidcrystal drip device according to claim 15, wherein the rotary valve bodyselectively communicates the syringe with a liquid crystal reservoir viathe valve hole of the rotary valve body to supply the liquid crystalstored in the liquid crystal reservoir to the syringe.
 17. The liquidcrystal drip device according to claim 15, wherein the dispenser movesthe plunger to drip the liquid crystal on said at least either one ofthe first and second substrates when the syringe is in fluidcommunication with the nozzle, and wherein the dispenser moves theplunger to supply the liquid crystal to the syringe when the syringe isin fluid communication with a liquid crystal reservoir.